Tag: David Archer

Something (early) for the weekend: grim forecast for oceans and the roots of denial

Something of a miscellany today, coupled with an open thread, to keep you going during a brief pause in posting. First up: a study published this week in PLOS Biology looks at changes in ocean chemistry, temperature and primary productivity over the next century under two emissions scenarios, and finds that no corner of the ocean escapes untouched. From Science Daily:

“When you look at the world ocean, there are few places that will be free of changes; most will suffer the simultaneous effects of warming, acidification, and reductions in oxygen and productivity,” said lead author Camilo Mora, assistant professor at the Department of Geography in the College of Social Sciences at the University of Hawai’i at Mānoa. “The consequences of these co-occurring changes are massive — everything from species survival, to abundance, to range size, to body size, to species richness, to ecosystem functioning are affected by changes in ocean biogeochemistry.”

It’s been a productive few weeks for Mora: he was lead author on a recent study ((Full text, free!)) published in Nature that estimated when climate in different parts of the world would move beyond anything experienced in the last 150 years — have a play with this interactive map to find out when your part of the world will move into the unknown. See also Climate Central, Science Daily, and a huge amount of press coverage.

Continue reading “Something (early) for the weekend: grim forecast for oceans and the roots of denial”

The Climate Crisis

The Climate Crisis: An Introductory Guide to Climate Change

David Archer and Stefan Rahmstorf are notable climate scientists. They are also excellent communicators of the science to the general reader, as is apparent in their new book The Climate Crisis: An Introductory Guide to Climate Change. My review of Archer’s previous book The Long Thaw remarked on his ability to illuminate topics for the non-scientist. In this book the authors seek to provide an accessible and readable account of the “treasure trove” of the IPCC reports. They distinguish their work sharply from the Summaries for Policy Makers officially provided by the IPCC, which are negotiated between government representatives and exclude much of what scientists think and write in the full report. But while they draw heavily on the latest IPCC report and feature many of its informative graphs and tables, they also refer to new findings since the 2006 cut-off date for the report, and draw attention to weaknesses they sometimes see in the report.

Most of the book deals with global climate science, the focus of IPCC Working Group I, with subsequent brief attention given to the impacts of climate change (Working Group II) and to mitigation (Working Group III).

After looking back over the development of the science from its slow beginnings in the 19th century with the discoveries of Fourier, Tyndall and Arrhenius to the explosion of research in more recent years, the authors carefully explain the way in which the global temperature responds to the forcings of the various agents, warming in the case of the greenhouse gases, offset by some cooling through the effect of aerosols. There are no natural forcings, such as solar irradiance, that can explain the warming of the past five decades.

The global average warming of 0.8 degrees since the late nineteenth century and 0.6 degrees since the 1970s is unequivocally shown by measurements.  Other observed changes include significant changes in rainfall, both increases and decreases, and some changes in atmospheric circulation patterns.

A chapter on ice and snow acknowledges the uncertain scientific understanding of the behaviour of melting ice on the ice sheets of Greenland and the West Antarctic and the unpredictability of ice sheet flow. The faster than expected sea ice melting in the Arctic carries profound climatic implications.  Overall observations of snow and ice provide powerful support for the warming trend.

The oceans receive attention as a major player in the climate pattern. We know that they are heating up, to some degree lessening the warmth in the atmosphere – the authors calculate a temporary effect of 0.4 degrees.  Salinity is being affected – increasing in sub-tropical regions and declining in higher latitudes.  Sea level is rising steadily, albeit with regional natural oscillations. The speed with which the ocean is taking up large amounts of CO2 from the atmosphere is making the water more acidic, a worrying trend likely to cause a severe threat to marine life if it continues.

Paleoclimatology studies support a key role for CO2 in regulating climate. They also tell us that Earth’s climate has the potential to flip abruptly from one mode of operation to another. They serve as a reality check for the climate models used to forecast Earth’s response to our CO2 release. The past strengthens the forecast.

The forecast is for warming somewhere between 2 degrees and 7 degrees depending on the IPCC scenario.  The authors regard it as unfortunate that all the IPCC scenarios are non-mitigation scenarios, intended to tell us what might happen if we do not take action to reduce emissions. They consider it a serious shortcoming that mitigation scenarios have not also been systematically assessed, though they are likely to be part of the next IPCC report. Other forecasts include changes in precipitation, which they note will probably have a bigger impact on human society and ecosystems than temperature changes. Sea level rise is likely to be higher than the limited forecast of the IPCC report, and the authors don’t rule out a rise by over one metre by the end of the century, noting that Hansen fears two metres by that date. Changes in ocean currents are uncertain and the authors at this point comment on the limitations of the use of climate models, also apparent in relation to ice sheet behaviour.  The low probability-high impact risks are difficult to assess. There may be a less than 10% risk of a shut-down of the Atlantic overturning circulation, but it would result in a massive change in the operation of the planet’s climate system. Ocean acidification will continue and worsen.

Against the accusation that the outlooks are alarmist they point to earlier IPCC projections which have turned out to be correct in the subsequent 18 years. In fact the faster than expected sea level rise and arctic sea-ice shrinking suggests that the IPCC in the past may have underestimated rather than exaggerated climate change, though they advance that possibility with caution.

In the last third of the book the authors move to discuss the impacts of climate change and how we might avoid it.  The expected impact on the world’s ecosystems is dire. Human society will suffer from water stress, from food insecurity, from coastal zone hazards due to rising sea level and from threats to health.  Adaptation will be necessary and can be very effective, but has no hope of coping with all the projected effects, especially over the long term. Mitigation is essential.  The book runs through some of the mitigation options offered by Working Group III.  However, noting that the consensus view the IPCC represents is regarded by some energy experts and engineers as too limited and conservative, the authors depart from the IPCC material for a time to provide a somewhat more visionary perspective, based on renewables, cogeneration, smart grids, heat pumps and electromobility. They refer to the surprise success story of wind power and look to a time later in the century when solar power could easily provide most of our energy needs.

In a final brief section the authors leave the IPCC to discuss policy matters.  In the course of the discussion they comment on the persistence of arguments against anthropogenic global warming which float around the internet and are repeated by gullible newspaper editors and systematically promoted by lobbyist organisations.

“We would personally be very relieved if anthropogenic global warming were to be disproven by some new scientific findings – we certainly do not “like” global warming. But at this point, the body of scientific evidence is so strong that the hope that this problem will go away by itself looks exceedingly remote…The good news is: we have the technological and economic capacity to meet this challenge.”

My background is teaching English and I appreciated seeing the book end with a lengthy quote from novelist Ian McEwan, known for his concern over climate change. He concludes:

“Are we at the beginning of an unprecedented sera of international cooperation, or are we living in an Edwardian summer of reckless denial? Is this the beginning, or the beginning of the end?”

One hopes for a wide readership for this measured book which clearly and thoughtfully sets out the results of the work of a great many scientists. I’m not sure that rationality stands much of a chance in a world which gives high popularity ranking to the denialism of authors like Booker and Plimer and Singer, but for those readers who retain a desire to understand real science Archer and Rahmstorf are reliable and helpful guides.

The Long Thaw

The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth's Climate

The legacy of our release of fossil fuel CO2 to the atmosphere will be long-lasting. It will affect the Earth’s climate for millenia. We are becoming players in geologic time. That is the conclusion that climatologist David Archer shares with a general audience in his newly published book The Long Thaw: How Humans Are Changing the Next 100,000 Years of Earth’s Climate.

The author is a professor in the Department of The Geophysical Sciences at the University of Chicago and a contributing editor at Real Climate. His book is relaxed in style, almost conversational sometimes, repetitive on occasion, but nevertheless closely focused and packed with instructive detail. It was a pleasure for a non-scientist like me to read. He seems to understand how to illuminate processes for the general reader. For example, his chapter on the distribution of carbon in the atmosphere, the land and the ocean, and his explanation of the interactions between them in the carbon cycle, provided angles and information that pulled together satisfyingly the bits and pieces of my hesitant understanding.   Similarly what he writes about the acidifying of the ocean by CO2 and the part calcium carbonate plays in slowly neutralising its effect is a model of lucidity.

The book’s structure is simple.  There are three sections.  The first describes the situation we are in right now – meaning the 20th and 21st centuries.  The second section is about the past, investigated as a forecast for the future.  The final section looks into the deep future.

Archer produces no surprises about our current situation.  The basic physics of the greenhouse effect – that gases in the atmosphere that absorb infrared radiation could eventually warm up the surface of the earth – was described in 1827 by the French mathematician Fourier. Then in 1896 Swedish chemist Arrhenius estimated the amount of warming that the Earth would undergo on average from a doubling of the atmospheric CO2 concentration – what we now call the climate sensitivity. Such work sets the scene for the climate science which has exploded in the past few decades as global warming grew from a prediction into an observation.    He describes many aspects of our current understanding of global warming, with several particularly helpful sequences, such as that on the relative strengths of four external agents of climate change called climate forcings – greenhouse gases, sulfur from burning coal, volcanic eruptions, changes in intensity of the sun. The warming that is occurring cannot be explained by natural forcings.  Looking ahead in the present century he is very aware that sea level rise by 2100 may well be higher than predicted by the IPCC, as it begins to appear that the ice models used to forecast may be too sluggish to predict the behaviour of real ice.

In the second section he moves steadily back in time, starting with the last 100,000 years where the abruptness of some of the changes detected leads him to reflect that the IPCC forecast of a smooth rise in temperature from 0.5 degrees excess warmth today  to about 3.0 degrees excess warmth in 2100 represents a best-case scenario in that it contains no unfortunate surprises. He then treats the longer-term glacial climate cycles through the last 650,000 years, paying attention to orbital forcing and to the ups and downs of atmospheric CO2 through the cycles.  He envisages the ice sheets and CO2“entwined in a feedback loop of cause and effect, like two figure skaters twirling and throwing each other around on the rink.” His final step back is to the hothouse world of 50 million years ago and beyond that to transitions between hothouse and ice age climates over 500 million years. He selects the Paleocene Eocene Thermal Maximum event (recently discussed on Hot Topic) as an analogue for the global warming future.

The third section looks at that future.  In discussing the land’s and ocean’s ability to take up carbon being released from fossil fuels he considers it likely that there are limits to that process which will mean that a significant fraction of fossil fuel CO2 will remain in the atmosphere for millenia into the future.  There are calming effects from the carbon cycle, but there can also be opposite effects as seems likely to have been the case at times in the past.  Hopefully large scale methane hydrate release won’t be a large part of such feedbacks, but if the ocean gets warm enough it is possible and could double the long-term climate impact of global warming.

For now the carbon cycle is responding to the CO2 increase by inhaling the gas into the ocean and high-latitude land surface, damping down the warming effect. But on the timescale of centuries and longer the lesson from the past is that this situation could reverse itself, and the warming planet could cause the natural carbon cycle to exhale CO2, amplifying the human-induced climate changes.

The clearest long-term impact of fossil-fuel CO2 release is on sea level rise.  The book has a restrained chapter on this, but there is no escaping what will happen if the ice sheets melt. “We have the capacity to ultimately sacrifice the land under our feet.“

Have we averted an ice age?  Archer discusses this possibility, but finds the evidence uncertain.  He would in any case not put such a possibility forward as an argument in favour of CO2 emissions. All it means is that natural cooling driven by orbital variation is unlikely to save us from global warming – at this stage the much greater danger. Incidentally he mentions Ruddiman’s book Plows, Plagues, and Petroleum briefly and appreciatively in this section, but gives reasons for doubting its conclusions. (The book was reviewed on Hot Topic recently.)

In his epilogue on economics and ethics, where he ponders whether we are likely to turn away from the path we are currently on, he offers a comparison with slavery, another ethical issue: “Ultimately it didn’t matter whether it was economically beneficial or costly to give up. It was simply wrong.”

James Hansen describes the book as the best about carbon dioxide and climate change that he has read.  “David Archer knows what he is talking about.” To which I would add that he also knows how to explain it clearly to anyone prepared to give him reasonable attention.