Hot off the press is a new global climate change synthesis report by some of the world’s leading scientists. The Copenhagen Diagnosis: Updating the World on the Latest Climate Science is a review of the hundreds of scientific papers published since the 2007 IPCC fourth assessment report (AR4), and presents a sobering update on the state of the global climate. What this report convincingly shows, is that AR4 was perhaps too conservative in its projections and warnings on the state of the climate. This document is intended to inform policy makers and the public ahead of the COP-15 round of climate change negotiations in Copenhagen on the state of climate change science.

The report is very accessible to a non-scientific audience, and I encourage you to have a read through the document (or at least the executive summary). Here I would like to present some of the report’s findings that I found most interesting:

Is climate change real?

- The IPCC AR4 made clear that evidence showing that humans were causing climate change was unequivocal, and the Diagnosis echoes this sentiment: “No credible scientific literature has been published since the AR4 assessment that supports alternative hypotheses to explain the warming trend” (p. 14). The Diagnosis goes on to talk about some common misconceptions about the climate and debunks the usual climate skeptic talking points.

Recent reports by mainstream media,  subsequently seized upon by climate change skeptics, such as certain Washington Post columnists, have highlighted ‘evidence’ that over the past 10 years global temperatures have not increased. This has been seized upon as proof that global warming doesn’t exist. Cherry-picking a few years from the temperature record and claiming that this proves global warming is a hoax ignores the influence of natural climate variability on the global climate.

Source: The Copenhagen Diagnosis, 2009, p. 15. Based on NASA GISS global temperature dataset.

As you can see from the above graph depicting the change in global temperature deviation over time, the temperature change between the year 2000 and the year 2008 in nearly identical, but when viewed over a 25 year timeframe (the minimum suggested by the IPCC to mask the ‘noise’ of climate variability’) you can see a clear upward trend.

- Other claims by skeptics that changes in solar radiation are to blame for the warming are contrary to observed measurements that “winters are warming more rapidly than summers, and overnight minimum temperatures have warmed more rapidly than the daytime maxima – exactly the opposite of what would be the case if the sun were causing the warming.” (p. 16)

Overall the Diagnosis shows that:

- This century, every year (2001-2008) has been one of the top 10 warmest years since temperature measurements began.

- Global CO2 emissions are trending near the higher emission scenarios that the IPCC AR4 considered.

- The oceans have absorbed an estimated 50% more heat than previous calculations, with global ocean temperatures the warmest on record this past summer.

- Worldwide, sea levels are rising 80% faster than expected since satellite measurements began in 1993, and sea-level rise is likely to be twice as high as projected in AR4 – with a 2 meter rise by 2100 as the upper limit of revised projections. See graph below.

Source: The Copenhagen Diagnosis, 2009, p. 39. The tide gauges dataset (in red) is based on Church and White 2008, and the satellite observations are based on Cazenave et al. 2008.

- Warming in the Arctic is unprecedented in the last 2000 years (discussed in detail in a previous post), and has reversed a cooling trend from changes in orbital cycles. As the graph below shows, the loss of Arctic sea ice is trending much greater than the range of IPCC models in AR4, and it is now very likely that the Arctic will be seasonally ice-free within the coming decades.

Source: The Copenhagen Diagnosis, 2009, p. 32. Based on Stroeve et al. (2007), updated to include data for 2008.

And finally, the kicker:

- “When the Earth last was 2-3 °C warmer than now, during the Pliocene 3 million years ago, sea level was 25-35 meters higher due to the smaller ice sheets present in the warmer climate.” (p. 47)

The Conclusion

The authors of the report argue that global GHG emissions need to peak between 2015 and 2020 in order avoid warming above 2 degrees C, a dangerous level where major societal and environmental disruptions would be expected. Business as usual emission growth scenarios put us breaching the 2 degree C threshold towards the middle of the century.

If anything, this report highlights that the last IPCC assessment was too conservative in its assumptions as to how quickly some earth systems would react to increased GHG levels. Hopefully the decision makers meeting in a few weeks will realize that the climate is changing faster than anticipated, and recognize the importance of rapidly mitigating global emissions. Unfortunately, political will (particularly in the U.S.) seems to be moving at glacial speeds.

Oh wait, glaciers are melting.

Source:

The Copenhagen Diagnosis, 2009:  Updating the World on the Latest Climate Science.  I. Allison, N.L. Bindoff, R.A. Bindschadler, P.M. Cox, N. de Noblet, M.H. England, J.E. Francis, N. Gruber, A.M. Haywood, D.J. Karoly, G. Kaser, C. Le Quéré, T.M. Lenton, M.E. Mann, B.I. McNeil, A.J. Pitman, S. Rahmstorf, E. Rignot, H.J. Schellnhuber, S.H. Schneider, S.C. Sherwood, R.C.J. Somerville, K. Steffen, E.J. Steig, M. Visbeck, A.J. Weaver.  The University of New South Wales Climate Change Research Centre (CCRC), Sydney, Australia, 60pp.

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