Thursday, November 26, 2009

The Copenhagen Diagnosis: Climate Science Report (or What's Been Happening Since the Last IPCC Report?)

‘The Copenhagen Diagnosis’ is a special report prepared by 26 climate researchers, most of whom are authors of published IPCC reports. In it they conclude "that several important aspects of climate change are occurring at the high end or even beyond the expectations of only a few years ago."

The text of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) was drafted more than three years ago, and since then "many hundreds of papers have been published on a suite of topics related to human-induced climate change." Therefore, the purpose of this new report is to "synthesize the most policy-relevant climate science published" in that time. According to the authors, the rationale is two-fold:

First, the report "serves as an interim evaluation of the evolving science midway through an IPCC cycle - IPCC AR5 is not due for completion until 2013."

Second, and the authors believe the most important, the report "serves as a handbook of science updates that supplements the IPCC AR4 in time for Copenhagen in December 2009, and any national or international climate change policy negotiations that follow."

Purposefully targeting readership by policy-makers, stakeholders, the media and the broader public, each section of the report "begins with a set of key points that summarises the main findings." The authors note that the "science contained in the report is based on the most credible and significant peer-reviewed literature available at the time of publication."

From the Executive Summary, the most significant recent climate change findings are:

Surging greenhouse gas emissions: Global carbon dioxide emissions from fossil fuels in 2008 were nearly 40 percent higher than those in 1990. Even if global emission rates are stabilized at present-day levels, just 20 more years of emissions would give a 25 percent probability that warming exceeds 2°C, even with zero emissions after 2030. Every year of delayed action increases the chances of exceeding the 2°C warming.

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 10 years, despite a decrease in solar forcing, the trend continues to be one of warming. Natural, short-term fluctuations are occurring as usual, but there have been no significant changes in the underlying warming trend.

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: Summertime melting of Arctic sea ice has accelerated far beyond the expectations of climate models. The area of sea ice melt during 2007-9 was about 40 percent greater than the average prediction from IPCC AR4 climate models.

Current sea level rise underestimated: Satellites show recent global average sea level rise (3.4 millimeters per year over the past 15 years) to be around 80 percent 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 the Working Group 1 of the IPCC AR4; for unmitigated emissions it may well exceed one meter. The upper limit has been estimated as about two meters sea level rise by 2100. Sea level will continue to rise for centuries after global temperatures have been stabilized, 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 (e.g. continental ice sheets, Amazon rain forest, 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 preindustrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a de-carbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – needs to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under one metric ton CO2 by 2050. This is 80-95 percent below the per-capita emissions in developed nations in 2000.

Clearly the time to act is now.

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