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NASA's Earth Science News Team

This video shows aerosol emission and transport from September 1, 2006, to April 10, 2007. Also included are locations, indicated by red and yellow dots, of wildfires and human-initiated burning as detected by the MODIS instrument on NASA's Terra and Aqua satellites. Credit: NASA Goddard Space Flight Center. Download the animation here.

The residents of Beijing and Delhi are not the only ones feeling the effects of Asian air pollution — an unwanted byproduct of coal-fired economic development. The continent's tainted air is known to cross the Pacific Ocean, adding to homegrown air-quality problems on the U.S. West Coast.

But unfortunately, pollution doesn't just pollute. Researchers at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, California, are looking at how Asian pollution is changing weather and climate around the globe.

Scientists call airborne particles of any sort — human-produced or natural — aerosols. The simplest effect of increasing aerosols is to increase clouds. To form clouds, airborne water vapor needs particles on which to condense. With more aerosols, there can be more or thicker clouds. In a warming world, that's good. Sunlight bounces off cloud tops into space without ever reaching Earth's surface, so we stay cooler under cloud cover.

But that simplest effect doesn't always happen. If there's no water vapor in the air — the air is dry — aerosols can't make clouds. Different types of aerosols have different effects, and the same aerosol can have different effects depending on how much is in the air and how high it is. Soot particles at certain altitudes can cause cloud droplets to evaporate, leaving nothing but haze. At other altitudes, soot can cause clouds to be deeper and taller, producing heavy thunderstorms or hailstorms. With so many possibilities, aerosols are one of the largest sources of uncertainty in predicting the extent of future climate change.

The experiments and result

During the last 30 years, clouds over the Pacific Ocean have grown deeper, and storms in the Northwest Pacific have become about 10 percent stronger. This is the same time frame as the economic boom in Asia. JPL researcher Jonathan Jiang and his postdoctoral fellow, Yuan Wang, designed a series of experiments to see if there was a connection between the two phenomena.

They used a numerical model that included weather factors such as temperature, precipitation and barometric pressure over the Pacific Ocean as well as aerosol transport — the movement of aerosols around the Earth. They did two sets of simulations. The first used aerosol concentrations thought to have existed before the Industrial Revolution. The other used current aerosol emissions. The difference between the two sets showed the effects of increased pollution on weather and climate.

An extra-tropical cyclone seen in the Pacific Ocean off the coast of Japan on March 10, 2014, by NASA's GPM Microwave Imager.

"We found that pollution from China affects cloud development in the North Pacific and strengthens extratropical cyclones," said Wang. These large storms punctuate U.S. winters and springs about once a week, often producing heavy snow and intense cold.

Wang explained that increased pollution makes more water condense onto aerosols in these storms. During condensation, energy is released in the form of heat. That heat adds to the roiling upward and downward airflows within a cloud so that it grows deeper and bigger.

"Large, convective weather systems play a very important role in Earth's atmospheric circulation," Jiang said, bringing tropical moisture up to the temperate latitudes. The storms form about once a week between 25 and 50 degrees north latitude and cross the Pacific from the southwest to the northeast, picking up Asia's pollutant outflow along the way.

Wang thinks the cold winter that the U.S. East endured in 2013 probably had something to do with these stronger extratropical cyclones. The intense storms could have affected the upper-atmosphere wind pattern, called the polar jet stream.

Jiang and Wang are now working on a new experiment to analyze how increased Asian emissions are affecting weather even farther afield than North America. Although their analysis is in a preliminary stage, it suggests that the aerosols are having a measurable effect on climatic conditions around the globe.

Conceptualizing Earth differently

How much these climate effects will increase in the coming decades is an open question. How much they can be reversed if emissions are reduced in Asia also remains unclear.

The researchers pointed out that their work should raise even more red flags about aerosol-based geoengineering solutions — interventions in the Earth system intended to counteract global warming. Some groups have suggested that we could inject sulfate aerosols into the stratosphere to block incoming sunlight, but Jiang and Wang found that sulfates are the most effective type of aerosol for deepening extratropical cyclones. Ongoing injections would bring more stormy winter weather globally and would likely change the climate in other ways we cannot yet foresee.

Jiang noted that Asian emissions have made him and some other climate researchers conceptualize Earth differently. "Before, we thought about the North-South contrast: the Northern Hemisphere has more land, the Southern Hemisphere has more ocean. That difference is important to global atmospheric circulation. Now, in addition to that, there's a West-East contrast. Europe and North America are reducing emissions; Asia is increasing them. That change also affects the global circulation and perturbs the climate."

http://climate.nasa.gov/news/2218/

NASA JPL Orbiting Carbon Observatory-2 satellite (OCO-2) can track CO2 back to its source, help refine model resolution to regions

Scientists will use measurements from the Orbiting Carbon Observatory-2 to track atmospheric carbon dioxide to sources such as these wildfires in Siberia, whose smoke plumes quickly carry the greenhouse gas worldwide. The fires were imaged on May 18, 2014, by NASA's Moderate Resolution Imaging Spectrometer instrument on the Terra satellite. Image credit: NASA/LANCE/EOSDIS Rapid Response 
› Larger image

NASA's JPL, July 18, 2014

NASA's Orbiting Carbon Observatory-2, which launched on July 2, 2014, will soon be providing about 100,000 high-quality measurements each day of carbon dioxide concentrations from around the globe. Atmospheric scientists are excited about that. But to understand the processes that control the amount of the greenhouse gas in the atmosphere, they need to know more than just where carbon dioxide is now. They need to know where it has been. It takes more than great data to figure that out.

"In a sense, you're trying to go backward in time and space," said David Baker, a scientist at Colorado State University in Fort Collins. "You're reversing the flow of the winds to determine when and where the input of carbon at the Earth's surface had to be to give you the measurements you see now."

Harry Potter used a magical time turner to travel to the past. Atmospheric scientists use a type of computer model called a chemical transport model. It combines the atmospheric processes found in a climate model with additional information on important chemical compounds, including their reactions, their sources on Earth's surface and the processes that remove them from the air, known as sinks.

Baker used the example of a forest fire to explain how a chemical transport model works. "Where the fire is, at that point in time, you get a pulse of carbon dioxide in the atmosphere from the burning carbon in wood. The model's winds blow it along, and mixing processes dilute it through the atmosphere. It gradually gets mixed into a wider and wider plume that eventually gets blown around the world."

Some models can be run backward in time -- from a point in the plume back to the fire, in other words -- to search for the sources of airborne carbon dioxide. The reactions and processes that must be modeled are so complex that researchers often cycle their chemical transport models backward and forward through the same time period dozens of times, adjusting the model as each set of results reveals new clues. "You basically start crawling toward a solution," Baker said. "You may not be crawling straight toward the best answer, but you course-correct along the way."

Lesley Ott, a climate modeler at NASA's Goddard Space Flight Center, Greenbelt, Maryland, noted that simulating carbon dioxide's atmospheric transport correctly is a prerequisite for improving the way global climate models simulate the carbon cycle and how it will change with our changing climate. "If you get the transport piece right, then you can understand the piece about sources and sinks," she said. "More and better-quality data from OCO-2 are going to create better characterization of global carbon."

Baker noted that the volume of data provided by OCO-2 will improve knowledge of carbon processes on a finer scale than is currently possible. "With all that coverage, we'll be able to resolve what's going on at the regional scale," Baker said, referring to areas the size of Texas or France. "That will help us understand better how the forests and oceans take up carbon. There are various competing processes, and right now we're not sure which ones are most important."

Ott pointed out that improving the way global climate models represent carbon dioxide provides benefits far beyond the scientific research community. "Trying to figure out what national and international responses to climate change should be is really hard," she said. "Politicians need answers quickly. Right now we have to trust a very small number of carbon dioxide observations. We're going to have a lot better coverage because so much more data is coming, and we may be able to see in better detail features of the carbon cycle that were missed before." Taking those OCO-2 data backward in time may be the next step forward on the road to understanding and adapting to climate change.

To learn more about the OCO-2 mission, visit these websites: http://www.nasa.gov/oco2 , http://oco.jpl.nasa.gov

http://www.jpl.nasa.gov/news/news.php?release=2014-237

Greenland: Dark Snow Project, 2014 field work season

by Greg Laden, Greg Laden's Blog, ScienceBlogs, May 14, 2014

The Dark Snow Project is staring up again, it being almost summer(ish) in Greenland.

The results in the study of the odd 2012 winter are now in. That year, there was a huge spike in melting on the surface of Greenland. (Discussed here.) One idea is that a good part of this melting was caused by extra soot from extensive wildfires in North America, which increased the amount of solar energy collected on the ice surface.

The results confirm this, and the Dark Snow team is returning this year to collect more information.

The Dark Snow project is crowd funded, and you are asked to provide a donation. More information on that here.

http://scienceblogs.com/gregladen/2014/05/14/dark-snow-project/

Waving goodbye to Judith Curry's Stadium Wave Model: About that global warming hiatus

by Greg Laden, ScienceBlogs, April 8, 2014

[This post was quite long, so I excerpted it; if you want all the details, please go to the link at the bottom of the post.]

Some of the variation in surface warming has been attributed by some researchers to a phenomenon known as the Atlantic Multidecadal Oscillation (AMO). “Oscillations” are a common phenomenon in climatology. Generally speaking, this is where a major variable (temperature or air pressure) in a given area or between two areas shifts back and forth around a mean. The AMO in particular has been a bit difficult to figure out, or for that matter, to prove that it really even exists. Part of the problem is that a single oscillation, which involves seas surface temperatures over the Atlantic Ocean, may have a period of 40 or even 80 years. For this reason, the high quality record of surface temperature change allows us to only see a couple of full oscillations, and this makes it hard to characterize and even harder to explain causally.

According to Michael Mann, lead author of a paper just out addressing the pause and its relationship to the AMO, “Some researchers have in the past attributed a portion of Northern Hemispheric warming to a warm phase of the AMO. The true AMO signal, instead, appears likely to have been in a cooling phase in recent decades, offsetting some of the anthropogenic warming temporarily.”

One application to understanding recent changes in the rate of warming in the context of the AMO is the so-called “Stadium Wave.” This is an actual Stadium Wave, a phenomenon seen at sporting events: (see video)

...

The climate Stadium Wave idea as proposed by Judith Curry suggests that certain changes in surface conditions related to the AMO result in swings in surface temperature that actually explain the long term “global warming curve” enough to discount or reduce the presumed effects of global warming. Curry’s Stadium Wave is a kind of emergent property of climate, where this and that thing happens and results in a large effect because of compounding variables.

It’s complicated. Here is an abstract from a paper by M. G. Wyatt and J. A. Curry explaining it:

A hypothesized low-frequency climate signal propagating across the Northern Hemisphere through a network of synchronized climate indices was identified in previous analyses of instrumental and proxy data. The tempo of signal propagation is rationalized in terms of the … Atlantic Multidecadal Oscillation. Through multivariate statistical analysis of an expanded database, we further investigate this hypothesized signal to elucidate propagation dynamics. The Eurasian Arctic Shelf-Sea Region, where sea ice is uniquely exposed to open ocean in the Northern Hemisphere, emerges as a strong contender for generating and sustaining propagation of the hemispheric signal. Ocean-ice-atmosphere coupling spawns a sequence of positive and negative feedbacks that convey persistence and quasi-oscillatory features to the signal. Further stabilizing the system are anomalies of co-varying Pacific-centered atmospheric circulations. Indirectly related to dynamics in the Eurasian Arctic, these anomalies appear to negatively feed back onto the Atlantic‘s freshwater balance. Earth’s rotational rate and other proxies encode traces of this signal as it makes its way across the Northern Hemisphere.

This led to a number of statements and predictions by Curry, which have been parsed out here.

For the past 15+ years, there has been no increase in global average surface temperature…
The stadium wave hypothesis provides a plausible explanation for the hiatus in warming and helps explain why climate models did not predict this hiatus. Further, the new hypothesis suggests how long the hiatus might last.
The ‘hiatus’ will continue at least another decade
Climate models are too sensitive to external forcing
Hiatus persistence beyond 20 years would support a firm declaration of problems with the climate models
Incorrect accounting for natural internal variability implies: Biased attribution of 20th century warming [and] Climate models are not useful on decadal time scales

...

Mann, Steinman and Miller, in their new paper, tried something interesting. They recreated a set of scenarios in which they could observe the AMO and other climate variables over time, but rather than having the AMO be a variable subject to emergence after other factors are accounted for, they introduced a known AMO. This way they could see the exact effects of the AMO on surface temperatures and other variables and explore the relationship between the variables. They call this the “differenced-AMO approach.” Knowing the true AMO signal, they were able to produce a correct climate signal, and when the AMO signal was detrended in this scenario, the final result failed to match known internal variability. In other words, using the previously applied techniques, such as used by Curry, the modeling did not work. More importantly, the detrended AMO signal had an artificially increased amplitude, with lower lows and higher highs, and these peaks occurred at the wrong times.

...

 The previously used detrending also missed the contribution of other factors that probably make the AMO look like something it isn’t. There have been a number of other effects on surface temperatures that are left behind after anthropogenic warming is detrended out of the data, especially the effects of sulfate aerosols, which come from power plants and such. “These aerosols have cooled substantial regions of the Northern Hemisphere continents in recent decades, thus masking some of the warming we otherwise would have seen,” Mann told me. “But aerosols have tailed off in recent decades thanks to the Clean Air Acts, etc. That has allowed the hidden warming to emerge in recent decades. If you subtract off a straight line from the temperature trend, you will appear to have an 'oscillation,' but that oscillation is just mostly due to the non-linear nature of the long-term forcing, with a substantial positive forcing (warming through 1950s, then slight warming or even cooling from the 1950s–1970s due to a large sulphate aerosol cooling contribution), followed by the accelerated warming in recent decades as aerosols have tailed off. We show in the paper that subtracting off a simple linear trend when you have this more complicated time history of human forcing of climate, gives rise to a spurious apparent 'oscillation.' ”

Go back, if you dare, to the abstract from Curry’s paper. Back when I used to teach multi-variate statistics for grad students (co-taught with a brilliant statistician, I quickly add) this is the kind of abstract we would look for to use in class. It demonstrates an all too common error, or at least potentially demonstrates it well enough to examine as an exemplar of what not to do. Climate systems are complex. There are a lot of known variables and accessible data sets, but those variables and data sets have often hidden relationships, or important factors are unknown, either entire variables or relationships between variables. If you take a set of possible causal variables and one or two ideal outcome variables, it is possible to mix and match among the candidate causal variables until you get a model that matches the outcome. Perhaps, in doing so, you’ve figured something out. Or, perhaps you just made up some stuff. One way to know if you’ve really explained a phenomenon is to have a sensible, even expected, physical process that links things together. In other words, you have a logical cause as well as a statistical link. The latter without the former is potentially wrong. A second way to evaluate your finding is to seek internal statistical or numerical relationships that result in apparent meaning but that are actually artifacts of your methods. In this case, Mann et al have done this; as demonstrated in this new paper, Curry’s stadium wave is one possible, but meaningless, outcome from the process of making statistical stone soup. Such is the way many theories of everything, large or small, seem to go.

Mann also told me that some of the other large scale oscillations that make up part of the standard descriptions of Earth climate systems could be subject to similar artifactual effects. It will be interesting to see if further work allows further refinement of our understanding of these systems over coming months or years. The models climate scientists use are pretty good, but this would make them more useful and accurate.

---

Mann, Michael, Byron Steinmann, and Sonya Miller. 2014. On Forced Temperature Changes, Internal Variability and the AMO. Geophysical Research Letters. DOI: 10.1002/2014GL05923

http://scienceblogs.com/gregladen/2014/04/08/waving-good-bye-to-the-stadium-wave-model-about-that-global-warming-hiatus/

Asian pollution climatically modulates mid-latitude cyclones following hierarchical modelling and observational analysis

Nature Communications, 5, article number 3098 (21 January 2014); doi: 10.1038/ncomms4098

Asian pollution climatically modulates mid-latitude cyclones following hierarchical modelling and observational analysis

• Yuan Wang,
• Renyi Zhang and
•  R. Saravanan

Abstract

Increasing levels of anthropogenic aerosols in Asia have raised considerable concern regarding its potential impact on the global atmosphere, but the magnitude of the associated climate forcing remains to be quantified. Here, using a novel hierarchical modelling approach and observational analysis, we demonstrate modulated mid-latitude cyclones by Asian pollution over the past three decades. Regional and seasonal simulations using a cloud-resolving model show that Asian pollution invigorates winter cyclones over the northwest Pacific, increasing precipitation by 7% and net cloud radiative forcing by 1.0 W m⁻² at the top of the atmosphere and by 1.7 W m⁻² at the Earth’s surface. A global climate model incorporating the diabatic heating anomalies from Asian pollution produces a 9% enhanced transient eddy meridional heat flux and reconciles a decadal variation of mid-latitude cyclones derived from the reanalysis data. Our results unambiguously reveal a large impact of the Asian pollutant outflows on the global general circulation and climate.

http://www.nature.com/ncomms/2014/140121/ncomms4098/full/ncomms4098.html

Climate change by the numbers: The worst is yet to come

CO2 levels went through the roof in 2013, as the world tried — and mostly failed — to slow down warming

by Lindsey Abrams, Salon, December 30, 2013

EnlargeFirefighters battle the Rim Fire near Yosemite National Park, Calif., on Aug. 25, 2013. (Credit: AP/Jae C. Hong/Salon)

“We will respond to the threat of climate change, knowing that the failure to do so would betray our children and future generations,” President Obama announced back in January at his second-term inauguration. Thus began another year of steady climate change, continued pollution of the atmosphere and half-hearted attempts at changing the world’s dire trajectory.

By many measures, 2013 wasn’t particularly extreme: it it wasn’t the hottest we’ve ever seen; its storms, by and large, weren’t the most devastating. Much of what occurred can best be seen as a sign of things to come. Droughts, believed to be exacerbated by climate change, will become more widespread. Wildfires are expected to get bigger, longer and smokier by 2050. Twelve months, after all, is but a short moment in Earth’s history. Only in the future, looking back, will we be able to recognize the true significance of many of this year’s big numbers:

7: Where 2013 ranks among the warmest years in history, according to the World Meteorological Association. Tied with 2003, the ranking is based on the year’s first nine months, during which average temperatures were 0.86 °F above the 1960-1991 global average.

395.5: The average concentration levels of CO2 in parts per million (ppm) observed in the atmosphere through November.

400: The ”milestone,” in parts per million of atmospheric CO2, that was temporarily crossed in May. It was the first time carbon levels crossed that boundary in 55 years of record-keeping — and possibly in 3 million years of history on Earth.

95: Percent certainty with which IPCC scientists say climate change is caused by human activity, a confidence level up from 90% in 1997.

1,100: Amount by which EPA regulations proposed in September would limit emissions from new coal-fired power plants, in pounds of CO2 per hour. The average plant currently emits CO2 at a rate of 1,800 pounds per hour.

25: The factor by which the concentration of PM 2.5 — the part of air pollution most harmful to human health — exceeded the amount considered safe in the U.S. when Beijing’s first “airpocalypse” occurred in January

1,000: Air pollution levels in the Chinese city of Harbin, in micrograms per cubic meter of PM 2.5, during October’s smog emergency. According to the World Health Organization, it shouldn’t exceed 20; anything higher than 300 is considered hazardous.

8: Age of girl in Harbin who contracted lung cancer.

3.8: Percent by which Japan said it would try to reduce its emissions by 2020, down from its  previous pledge of 25%.

1.97 million: The annual minimum extent of Arctic sea ice, in square miles. Melting this year wasn’t as severe as it was in 2012, but the remaining area was still 17% below average — and the sixth lowest on record.

3.2: Current average sea level rise, in millimeters per year. Sea levels reached a record high in March.

104.6: The average country-wide temperature, in degrees Fahrenheit, on January 7 in Australia — the continent’s hottest day on record, in its hottest month on record.

121.3: The temperature reading, in degrees Fahrenheit, in the South Australian town of Moomba on January 12.

90: Percent confidence with which researchers at the University of Melbourne concluded, in July, that “human influences on the Australian atmosphere had dramatically increased the odds of extreme temperatures.”

129.2: The temperature, in degrees Fahrenheit, recorded in California’s Death Valley on June 30, setting a record for the hottest temperature ever recorded on Earth for that month.

2: The weather emergency level declared by officials in China during this summer’s heat wave — a number normally reserved for typhoons and floods.

1.7 billion: The estimated cost, in USD, of New Zealand’s drought — its worst in 30 years.

10: The number of consecutive months during which over half of the contiguous U.S. experienced moderate or severe drought, which finally fell below 50% in mid-April 2013.

72: Percent of land area in 10 Western states in drought conditions after a record-breaking heat wave in June.

3.95: Inches of rain that fell from January to November in San Francisco. When the final numbers come in, it’s likely that California will be found to have had its driest year on record.

257,000: Acres of land burned by the California Rim Fire, the biggest wildfire in Sierra’s recorded history, which caused over $50 million in damage. It was caused by a number of factors, drought and abnormal seasons included.

5.9–7.9: The amount of rain, in inches, that normally falls over two and a half months and instead pummeled central Europe between May 30 and June 1. Floodwaters in Germany rose to their highest levels in over 500 years.

1.3: The width, in miles, of the tornado that struck Moore, Oklahoma on May 20. Sen. Sheldon Whitehouse, D-R.I., caused controversy when he invoked the storm during a speech criticizing climate deniers. While researchers cannot be sure there was a link between climate change and the twister, they believe that a warming planet may host more frequent, stronger storms.

2.6: The width, in miles, of the tornado that struck El Reno, Oklahoma, 10 days later. It was the widest ever measured on Earth.

20 billion: Cost, in dollars, of plans laid out by NYC Mayor Bloomberg in June to make infrastructure improvements, including floodwalls and storm barriers, in preparation for the effects of climate change.

6,100: The most recent death count from Typhoon Haiyan, which officially became the deadliest storm in Philippines’ history. Bodies continue to be recovered.

132: The number of countries that walked out of the U.N. climate talks in Warsaw in protest over rich nations’ refusal to entertain the idea of compensation for extreme climate events

90: The number of global companies that together account for two-thirds of greenhouse gas emissions, according to a report in the journal Climactic Change.

7 billion: The number of “key individuals” responsible for climate change. The Onion, as always, is spot on.

http://www.salon.com/2013/12/29/climate_change_by_the_numbers_the_worst_is_yet_to_come/

China Uncensored (Beijing's Most Dangerous Pastime—Breathing): Air pollution so bad the spy cameras can't see anything

Beijing's Most Dangerous Pastime—Breathing

from China Uncensored: Beijing is being gassed with "crazy bad" air pollution. Did I say air pollution? I meant to say, "heavy fog." That's what China's media calls it. But don't think that doesn't mean the Chinese regime isn't doing anything about it! The smog has made it next to impossible to spy on people! What good are China's network of more than 20 million cameras if they can't see through toxic clouds of smog that can be seen from outer space!?!

https://www.youtube.com/watch?v=oR8d1PZvYRI

David Spratt: Is climate change already dangerous? Part III. Consequences from current greenhouse gas levels

by David Spratt, Climate Code Red, September 22, 2013

Third in a series

Danger from implied temperature increase

The current level of atmospheric CO2 only is sufficient to increase the global temperature at equilibrium by +1.5 °C, based on the standard assumption of near-term climate sensitivity of 3 °C for doubled CO2.

If all current greenhouse gases are taken into account, then: 

The observed increase in the concentration of greenhouse gases (GHGs) since the pre-industrial era has most likely committed the world to a warming of 2.4 °C (within a range of +1.4 °C to +4.3 °C) above the pre-industrial surface temperatures (Ramanthan and Feng).

And the 2007 IPCC Synthesis report (Table 5.1 on emission scenarios) also shows that for levels of greenhouse gases that have already been achieved (CO2 in the range of 350–400 ppm, CO2e in the range 445–490 ppm) and peaking by 2015, the likely temperature rise is in the range of 2–2.4 °C. 

These scenarios include short-lived gases such as methane, which degrades out of the atmosphere in a decade, and also nitrous oxide, which has an atmospheric lifetime of around a century. On the other hand, the fact that temperatures are not already much higher than they are today is due principally to the large-scale emission of very short-lived (10 days) aerosols, such as soot and exhaust from burning fossil fuels, industrial pollution, and dust storms, which are providing temporary cooling. The effect is known popularly as “global dimming,” because the overall aerosol impact is to reduce, or dim, the sun’s radiation, thus masking some of the heating effect of greenhouse gases. The aerosol impact is not precisely known, but Ramanthan and Feng estimate it as high as ~1 °C. As the world moves to low-emission technologies, most of the aerosols and their temporary cooling will be lost. Recent research finds that quickly eliminating all greenhouse gas emissions (and necessarily the associated aerosols) would produce warming of between 0.25 and 0.5 °C over the decade immediately following (Matthews and Zickfield; Hansen, Sato et al.).

A practical consideration of “dangerous” can include the question as to whether there are tipping points or “concerns” activated for the elevated temperatures that we are generally considered to be already committed to: conservatively in the range say +1.5 to 2 °C and, more pragmatically, in the range of 2 to 2.4 °C if all current greenhouse gases are considered. A related question is whether the +1.5 °C goal advocated by the small island states and surveyed recently by Climate Action Network Europe and Climate Analytics would avoid “dangerous” climate change and significant tipping points.

This is a broad topic, but four recent important research findings on impacts for the current committed warming are arresting:

Greenland Ice Sheet tipping point

The tipping point for GIS has been revised down by Robinson, Calov et al. to +1.6 ºC (uncertainty range of +0.8 to +3.2 ºC) above pre-industrial, just as regional temperatures are increasing at three-to-four times faster than the global average, and the increased heat trapped in the Arctic due to the loss of reflective sea ice ensures an acceleration in the Greenland melt rate.  If the lower Greenland boundary in the uncertainty range turned out to be right, then with current warming of +0.8 ºC over pre-industrial we have already reached Greenland’s tipping point.  And, with temperature rises in the pipeline, the upward trajectory of annual greenhouse gas emissions, the projected future increases in fossil fuel use, and the continuing political impasse in international climate negotiations, we are very likely to hit the best estimate of +1.6 ºC within a decade or two at most.

Coral reefs

Frieler, Meinshausen et al. show that “preserving more than 10 per cent of coral reefs worldwide would require limiting warming to below +1.5 °C (atmosphere–ocean general circulation models (AOGCMs) range: 1.3–1.8 °C) relative to pre-industrial levels”.  Obviously at less than 10 per cent, the reefs would be remnant, and reef systems as we know them today would be a historical footnote.  Already, the data suggests that the global area of reef systems has already been reduced by half. A sober discussion of coral reef prospects can be found in Roger Bradbury’s “A World Without Coral Reefs” and Gary Pearce’s “Zombie reefs as a harbinger for catastrophic future.”  The opening of Bradbury’s article is to the point: 

It’s past time to tell the truth about the state of the world’s coral reefs, the nurseries of tropical coastal fish stocks.  They have become zombie ecosystems, neither dead nor truly alive in any functional sense, and on a trajectory to collapse within a human generation.  There will be remnants here and there, but the global coral reef ecosystem — with its storehouse of biodiversity and fisheries supporting millions of the world’s poor — will cease to be.

3c. Arctic carbon stores

As Climate Progress recently noted: “We’ve known for a while that ‘permafrost’ was a misnomer” because thawing permafrost feedback will turn the Arctic from a net carbon sink to a net source in the 2020s and defrosting permafrost will likely add up to 1 ºC to total global warming by 2100.   A 2012 UNEP report on policy implications of warming permafrost says the recent observations “indicate that large-scale thawing of permafrost may have already started.”  In February 2013, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates warned that a +1.5 ºC global rise in temperature compared to pre-industrial was enough to start a general permafrost melt.  Vaks, Gutareva et al. found that “global climates only slightly warmer than today are sufficient to thaw extensive regions of permafrost.” Vaks says that: “1.5 ºC appears to be something of a tipping point.”

Previously a study of East Siberian permafrost by Khvorostyanov, Ciais et al.  found that once mobilised, the process would be self-maintaining due to “deep respiration and methanogenesis” (formation of methane by microbes).  In other words, the microbial action that produces methane as the carbon stores melt would produce sufficient heat to maintain the process: “once active layer deepening in response to atmospheric warming is enough to trigger deep-soil respiration, and soil microorganisms are activated to produce enough heat, the mobilization of soil carbon can be very strong and self-sustainable.”

A sharp scientific debate has started on the stability of large methane clathrate stores just below the ocean floor on the shallow East Siberian Sea, following the publication in July 2013 of research by Whiteman, Hope and Wadhams which said that the release of a single giant “pulse” of methane from thawing Arctic permafrost beneath the East Siberian Sea could come with a $60 trillion global price tag. Wadhams says “the loss of sea ice leads to seabed warming, which leads to offshore permafrost melt, which leads to methane release, which leads to enhanced warming, which leads to even more rapid uncovering of seabed,” and this is not “a low probability event.”

Multiple targets reduce allowable warming

Steinacher, Joos et al. explore the interaction of targets in emissions reductions, focusing on the 2 ºC temperature goal. They find that when multiple climate targets are set (such as food production capacity, ocean acidity, atmospheric temperature), “allowable cumulative emissions are greatly reduced from those inferred from the temperature target alone.” In fact, “When we consider all targets jointly, CO2 emissions have to be cut twice as much as if we only want to meet the 2 ºC target.”

Lessons from climate history

Another fruitful line of inquiry on whether climate change is already “dangerous” is to look at the paleo-climate (climate history) record for circumstances analogous to present conditions to learn what planetary and climate conditions were like at that time.  With current CO2 levels at 400 ppm, a useful comparison is the Pliocene (3–5 million years ago).  The research body is large and growing in this area, but here are some examples:

Sea-levels

Rohling, Grant et al.  find that during the mid-Pliocene, when greenhouse gases were similar to today, sea levels were more than 20 metres higher than today “we estimate sea level for the Middle Pliocene epoch (3.0–3.5 Myr ago) – a period with near-modern CO2 levels – at 25 ±5 metres above present, which is validated by independent sea-level data.” Likewise Hansen, Sato et al. find that “during the middle-Pliocene… we find sea level fluctuations of 20–40 metres associated with global temperature variations between today’s temperature and +3 °C.”

Speed of sea-level rise

The speed of sea-level rise may far exceed the current, rather reticent estimates that are used for policy purposes.  Blancon, Eisenhauer et al. examined the paleo-climate record and showed a sea-level rises of 3 metres in 50 years due to the rapid melting of ice sheets 123,000 years ago in the Eemian, when the energy imbalance in the climate system was less than at present. 

Polar feedbacks

Hansen, Sato et al. find that current temperatures are at least as high as the Holocene Maximum (i.e., as high as they have been over the last 10,000 years).  They sum up: 

Earth at peak Holocene temperature is poised such that additional warming instigates large amplifying high-latitude feedbacks.  Mechanisms on the verge of being instigated include loss of Arctic sea ice, shrinkage of the Greenland ice sheet, loss of Antarctic ice shelves, and shrinkage of the Antarctic ice sheets.  These are not runaway feedbacks, but together they strongly amplify the impacts in polar regions of a positive (warming) climate forcing…  Augmentation of peak Holocene temperature by even +1 ºC would be sufficient to trigger powerful amplifying polar feedbacks, leading to a planet at least as warm as in the Eemian and Holsteinian periods, making ice sheet disintegration and large sea level rise inevitable.

[It is relevant here to note that warming in the pipeline due to thermal inertia, plus warming associated with the loss of aerosols, is greater than +1ºC.]

And during the Pliocene, with atmospheric greenhouse levels similar to today, the northern hemisphere was free of glaciers and ice sheets and beech trees grew in the Transantarctic Mountains. There are also strong indications that permanent El Nino conditions prevailed.

4d. Arctic carbon stores

As discussed above, scientists using radiometric dating techniques on Russian cave formations to measure historic melting rates going back 500,000 years conclude that a +1.5 ºC global rise in temperature compared to pre-industrial is enough to initiate widespread permafrost melt.  

In May this year, Brigham-Grette, Melles et al. published evidence from Lake El’gygytgyn, in north-east Arctic Russia, showing that 3.6–3.4 million years ago, summer mid-Pliocene temperatures locally were ~8 °C warmer than today, when CO2 was ~400 ppm.  This is highly significant because researchers including Celia Bitz and Philippe Ciais have previously found that the tipping point for the large-scale loss of permafrost carbon is around +8 ºC  to 10 ºC regional temperature increase.  Caias told the March 2009 Copenhagen climate science conference that: “A global average increase in air temperatures of +2 ºC and a few unusually hot years could see permafrost soil temperatures reach the +8 ºC threshold for releasing billions of tonnes of carbon dioxide and methane.” So, if the current level of greenhouse gases is enough to produce Arctic regional warming of ~+8 °C and that is a likely tipping point for large-scale permafrost loss, we have reached a disturbing milestone.

Even more disturbing is new research from Ballantyne, Axford et al. which says that during the Pliocene epoch, when CO2 levels were ~400 ppm, Arctic surface temperatures were 15–20 °C warmer than today’s surface temperatures. They suggest that much of the surface warming likely was due to ice-free conditions in the Arctic. Compared to the estimated tipping point for the large-scale loss of permafrost carbon of +8 ºC to 10 ºC regional warming, this research confirms both that the current level of greenhouse gases is sufficient to create both a sea-ice-free Arctic and Arctic warming more than sufficient to trigger large-scale loss of permafrost carbon.

Next post: Climate safety and the emissions reduction challenge 

http://www.climatecodered.org/2013/09/is-climate-change-already-dangerous-3.html