Tag: Rahmstorf

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.