With the Doha climate conference under way, Nature’s edition for 29th November devoted a special section to climate-related topics, but Science for 30th November was business as usual (does this reflect a US – UK divide?). Nature provides an editorialwhich makes the point that climate change and international agreements to limit it are travelling on different time-lines (I am not even sure that the agreements have any forward motion!), and points to the considerable benefit of increases to efficiency of energy use. One surprising statistic – the IEA estimates that efficiency increases between 1980 and 2010 reduced global demand by 35%, or about the amount of energy used today by the US and China combined. Four articles relating to the imminent end of Kyoto focus mainly on how little Kyoto has achieved, and on the need to learn and do better. This special section opens with a delightful view of Jiangxi province, China – talk about Mordor.
Jiangxi province, China. From News Feature, Nature 491, 29 Nov 2012. Image © Reuters
The present pattern of energy use, and the failure of Kyoto to curb use is shown in two graphics from these articles.
From: Q. Schiermeier, The Kyoto Protocol: Hot Air, Nature 491, 29 Nov 2012, Image © Netherlands Envir. Assessment Agency
From: Q. Schiermeier, The Kyoto Protocol: Hot Air, Nature 491, 29 Nov 2012, Image © Netherlands Envir. Assessment Agency
In the subscription-only portion of this issue of Nature, there is an article by K.M. Grant of University of Southampton and colleagues reporting their successful dating of a continuous, high-resolution sea-level record in millennial-scale detail throughout the past 150,000 years. They found that polar climate and ice-volume changes, and their rates of change were synchronized (within the ‘hundreds of years’ level of precision possible), and that rates of sea-level rise reached at least 1.2 m per century during all major episodes of ice-volume reduction. (Read that last sentence slowly again, because it suggests the rates of sea level rise we are seeing now are very likely to increase substantially!)
While Science did little special to mark the Doha climate conference, an article in the 30 November issue provided new information on ice, the main topic of this post. Scientists are beginning to get a good handle on the extent to which ice in various places is melting, and what that means for sea level rise and other aspects of climate change. Melting of the Arctic sea ice has garnered a lot of attention, and its record retreat last September made world-wide news. Melting of snow pack over terrestrial sites in the Arctic was the subject of a recent article in Geophysical Research Letters.
Image © Paul Souders/Corbis
Andrew Sheppard of Leeds University, and a slew of over 40 co-authors from all over, reported in Science on the mass-balance of Earth’s polar ice-caps. Using a variety of satellite altimetry, interferometry, and gravimetry techniques, they have been able to obtain and compare multiple separate estimates of the extent of the ice on northern and southern land masses. There was considerable agreement among the methods used, and the results show substantial melting in recent years. Over the last 20 years, more than 4 trillion tonnes of ice has melted from Greenland and Antarctica and drained into the ocean, contributing to sea level rise. To be precise, between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by -142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes per year, respectively (negative numbers denote melting, the East Antarctica ice sheet grew slightly during this time, while the others all melted).
Figure shows the rates of loss of ice, and the resulting increases in sea level for A) the three ice masses in Antarctica, and B) the ice masses for Greenland and all of Antarctica, plus the two combined. Taken from Sheppard et al. Science 338: 1183, 2012. Image © Science
These data are not surprising, but they do give new precision to the extent of ice mass lost to date, and will be valuable in testing and refining the ability of climate models to model rates of ice loss. In addition to providing more precise estimates of ice loss during the years since 1992, the study confirms that the rate of ice loss has been accelerating, particularly in Greenland where the current rate is five times that in the early 1990s. Like most Science articles this one requires a subscription for access, but Damien Carrington provides a good description of the study and its significance in The Guardian.
All the melting of ice and snow that is going on does several important things to the way our world behaves. Sea level rises, and Sheppard and his colleagues have been able to show that ice mass loss in Greenland and Antarctica has led to about 11 millimeters of sea level rise since 1992 – not much, but the rate is increasing rapidly. Secondly, the melt adds freshwater to polar oceans which, if sufficient is added, will cause noticeable drops in salinity. This may sound trivial, but the salinity and temperature of Arctic water flowing south into the Atlantic has a controlling effect on the rate at which warm Gulf Stream waters, flowing up from the tropics, cool and sink, carrying oxygen and heat to the deep ocean. I’ll take this story up at a later time. Thirdly, the melting ice leads to accelerated warming as darker, ice-free surfaces absorb more of the incident sunlight. This factor alone likely accounts for the very rapid rise in temperate that we are seeing in Arctic regions around the world. And this third consequence has run-on impacts on weather further south. And since I had to fire up my snow blower for the first time this week, winter weather is on my mind.
Until a couple of weeks ago, I naively assumed that with Arctic warming we could expect consistently warmer winters in North America and Eurasia. But then I visited Cornell University and happened to meet Charles Greene, a biological oceanographer and ecologist who has widened his view of the world to include ocean-atmosphere interactions and their effects on weather and climate. Chuck Greene has just published a very accessible article in Scientific American that deals with the effect of Arctic warming on weather in North America and Eurasia, an article which goes so far as to predict the kind of winter we are likely to experience in 2012-13. Nothing like sticking your neck out. Needless to say, the real world of the Arctic is way more complex than I assumed.
Two natural climate phenomena, the Arctic Oscillation and the North Atlantic Oscillation, play an important role in the weather of the northern hemisphere. They tend to oscillate in unison, and when they are both in their positive phase there is typically a greater absolute difference between the high pressure centers usually located over the subtropics, and the low pressure centers usually located in the subarctic. When they are in their negative phases, the difference in pressure between the high and the low centers is much less. In consequence, the polar vortex and the jet stream are both stronger and more regular in strength when the two oscillations are in positive phase, and weaker and more variable in path when the two oscillations are in negative phase. A more variable jet stream can bring cold Arctic air far south, or warm subtropical air far north. The warming of the Arctic due to loss of sea ice and other factors has resulted in an increase in the preponderance of negative phase Arctic and North Atlantic Oscillations. As a result, recent winters have been characterized by bouts of unusually cold weather, as well as periods of very warm weather, instead of being of more or less average weather through the season.
Taken from C.H. Greene, Scientific American, December, 2012. Image © Scientific American.
Greene notes that the past three winters in parts of North America and Europe were unusual. First, during the winters of 2009–2011, the eastern seaboard of the U.S. and western and northern Europe endured a series of exceptionally cold and snowy storms—including the February 2010 “snowmageddon” storm in Washington, D.C., that shut down the federal government for nearly a week. Later, despite the fact that NOAA, recognizing we were in a La Niña pattern (another oscillation in the Pacific), had forecasted a mild 2010–2011 winter for the eastern US, very low temperatures and record snowfalls hit New York City and Philadelphia in January 2011. In 2011–2012, the eastern U.S. had one of its mildest winters in history, while other parts of North America and Europe were less fortunate. The average January temperature across Alaska was 10oC below average, and an extended outbreak of frigid weather descended on central and eastern Europe, bringing temperatures of –30oC, snowdrifts that reached rooftops, and more than 550 deaths. Greene predicts periods of exceptional cold this coming winter, precisely because sea ice retreated so far last summer. Be on the lookout for Alberta Clippers.
Severe winter weather brings environmental and economic consequences. Farmers who depend on fruit trees that set their flower buds in the fall, ready to bloom in early spring have much to lose when an unseasonable warm spell in early spring is followed by more frost. That’s what happened in the north-east of North America this year. I hope it does not do so again in 2013.
Chuck Greene taught me something else with another article he shared with me. This also is quite accessible, in the on-line magazine, Solutions. In it, Greene and two colleagues explore the challenge of reducing CO2 concentration in the atmosphere to 350ppm, the concentration we enjoyed in the early 1980’s, and a level that environmental and climate scientists are now arguing needs to be reached to stabilize climate once more. (That the politicians, if they talk about limits at all, talk about 450 or 500ppm reveals the gap between what the science tells us and where the rest of the community is.) In their view, it is now virtually impossible to get to 350 without doing something beyond reducing CO2 emissions. They say we will have to also engage in some geoengineering. More about that later, the lesson I was taught in the opening pages was that we have more committed warming than I thought we did.
Committed warming is the warming we have committed to by our past actions, and it exists because the Earth is a big place and chemicals do not diffuse though the atmosphere, and exchange between the atmosphere, the ocean and the land instantaneously. There are delays and feedbacks, and together they ensure that when greenhouse gases are increasing in the atmosphere, there is a time delay before the warming that will be caused actually happens. So, we have succeeded in bringing the Earth’s atmosphere to 394ppm (seasonally corrected mean, October 2012), and if we kept it at that concentration from now on, the atmosphere will continue to warm for a while. That extra warming is the committed warming.
My prior understanding was that we had seen warming of about 0.8oC since the start of the industrial era, and that we were now committed to a further 1.2oC warming by the end of the century. Greene and colleagues set me right. We have already experienced 0.8oC, are committed to a further 1.6oC by 2100, but we are also committed to an additional 2.4oC or so over the next couple of hundred years. Some of those delays and feedbacks are very slow.
There is a big problem here. Just as the time delays lead to committed warming when CO2 levels are increasing, they lead to a delay in cooling when CO2 levels are lowered. This means that if we start working to lower emissions, and start lowering CO2 concentration in the atmosphere, the Earth will continue warming for a short while and its cooling will lag just as warming has up till now. This makes it more difficult to avoid the warmer world we have already committed to than it otherwise would.
In fact, we cannot suddenly stop increasing CO2 concentrations in the atmosphere, because we cannot stop all emissions overnight. And this is why the World Bank report I discussed in my last post talks about the 4oC world we are now set to experience. A week ago, I was optimistic that we might be on the verge of getting our global act together, but since then I have read some of Chuck Greene’s articles, have looked again at the amount we have to do to curtail warming, and have seen a report of comments by Peter Kent (Canada’s Minister of Environment) just prior to leaving for Doha. He will be bragging about Canada’s new emissions standards for cars (we confirmed the limits set by the US over a year ago, and continued to exempt light trucks = SUVs, so effectively did nothing that had not already been done to us by others). He will repeat his tiresome mistruth that Canada is halfway towards our 2020 emissions reduction goal. And he and the rest of our delegation will probably continue to play the role of spoiler, preventing any movement towards more effective policies. I hope I am wrong, but today I think we may be heading towards a 6oC world.
Greene’s solution to this dilemma is geoengineering, but not by spraying aerosols of sulfur into the atmosphere to dim the sun, or by spraying iron over the ocean to create algal blooms – spare a moment to commiserate again with the good folks of Haida Gwai who got ripped off on that one. Greene has some imaginative ideas that take advantage of the very high productivity of marine algae. I’ll save that story for a later time.