It is over three years since the drafting of text was completed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). …
The purpose of this report is to synthesize the most policy-relevant climate science published since the close-off of material for the last IPCC report. …
This report covers the range of topics evaluated by Working Group I of the IPCC, namely the Physical Science Basis. …
The authors primarily comprise previous IPCC lead authors familiar with the rigor and completeness required for a scientific assessment of this nature.
(The Copenhagen Diagnosis, 2009: Updating the World on the Latest Climate Science, 2009, p 5)
Contents
Land and Atmosphere
Ice and Ocean
Abrupt Change, Tipping Points, Past and Future Climate
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Climate Change Research Centre
- The Copenhagen Diagnosis, 2009: Updating the World on the Latest Climate Science, Climate Change Research Centre, The University of New South Wales, Sydney, 2009.
Ian Allison, Nathan Bindoff, Robert Bindschadler, Peter Cox,Nathalie de Noblet-Ducoudré, Matthew England, Jane Francis, Nicolas Gruber, Alan Haywood, David Karoly, Georg Kaser, Corinne Le Quéré, Tim Lenton, Michael Mann, Ben McNeil, Andy Pitman, Stefan Rahmstorf, Eric Rignot, Hans Joachim Schellnhuber, Stephen Schneider, Steven Sherwood, Richard Somerville, Konrad Steffen, Eric Steig, Martin Visbeck and Andrew Weaver.
Executive Summary
The most significant recent climate change findings are:- Recent global temperatures demonstrate human-induced warming:
- Over the past 25 years temperatures have increased at a rate of 0.19°C per decade, in very good agreement with predictions based on greenhouse gas increases.
Even over the past ten years, despite a decrease in solar forcing, the trend continues to be one of warming. …- Acceleration of melting of ice-sheets, glaciers and ice-caps:
- A wide array of satellite and ice measurements now demonstrate beyond doubt that both the Greenland and Antarctic ice-sheets are losing mass at an increasing rate.
Melting of glaciers and ice-caps in other parts of the world has also accelerated since 1990.- Rapid Arctic sea-ice decline:
- Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models.
The area of summertime sea-ice during 2007-2009 was about 40% less than the average prediction from IPCC AR4 climate models.- Current sea-level rise underestimated:
- Satellites show recent global average sea-level rise (3.4 mm/yr over the past 15 years) to be ~80% above past IPCC predictions.
This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps, and the Greenland and West-Antarctic ice-sheets.- Sea-level predictions revised:
- By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4; for unmitigated emissions it may well exceed 1 meter.
The upper limit has been estimated as ~2 meters sea level rise by 2100 … and several meters of sea level rise must be expected over the next few centuries. …- Delay in action risks irreversible damage:
- Several vulnerable elements in the climate system (eg continental ice-sheets, Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century.
The risk of transgressing critical thresholds (“tipping points”) increases strongly with ongoing climate change.
Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized. …- The turning point must come soon:
- If global warming is to be limited to a maximum of 2°C above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. …
To stabilize climate … average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050.
This is 80-95% below the per-capita emissions in developed nations in 2000.
