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Copenhagen Diagnosis Released, Detailing Accelerating Indicators of Climate Change In Last Three Years
25 November 2009
by Jack Rosebro
A team of 26 climate scientists from Australia, Austria, Canada, France, Germany, Switzerland, the United Kingdom, and the United States have published the “Copenhagen Diagnosis”, an interim synthesis report on developments in climate change science from mid-2006 to the present day. The report points out that many key harbingers of climate change “are occurring at the high end or even beyond the expectations of only a few years ago."”
Although the report is not an official Intergovernmental Panel on Climate Change (IPCC) document, many of its authors have served as lead authors of IPCC Assessment Reports in the past, and most of them have authored or co-authored seminal papers on climate change.
“The rationale [for the report] is two-fold,” the authors explain. “First, this report serves as an interim evaluation of the evolving science midway through an IPCC cycle: IPCC’s AR5 (Fifth Assessment Report) is not due for completion until 2013.” The most recent peer-reviewed papers evaluated by the authors of the Fourth Assessment Report (AR4) were published in mid-2006. Work published after then will be evaluated by the IPCC during the AR5 authoring cycle, which is just getting underway.
“Second, and 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.” In this sense, the report models itself on the efforts of Working Group 1 in the IPCC’s Assessment Reports, presenting no new data on climate change, but instead gathering and synthesizing existing scientific literature, and noting trends that have been confirmed by multiple sources.
Recent and significant climate change findings cited in Copenhagen Diagnosis include:
Emissions. Global carbon dioxide emissions from fossil fuels in 2008 were nearly 40% higher in 2008 than in 1990. This is roughly equal to the most severe emissions scenario yet considered by the IPCC, even though that scenario (A1, Fossil Intensive) was originally calculated as a reference baseline, absent any efforts towards emission reduction such as the Kyoto Protocol.
Concurrent with increased greenhouse gas (GHG) levels—now deemed higher than at any point in time in the last 800,000 years—the ability of natural oceanic and terrestrial carbon sinks to absorb CO2 from the Earth’s atmosphere appears to be deteriorating, having likely decreased by at least 5% in the past half century, although inter-annual variability is large.The degradation of natural carbon sinks amplifies the effects of climate change,
producing the same net effect on atmospheric concentrations of GHGs as increases in greenhouse gas emissions. Some specific carbon sinks, such as the Southern Ocean, appear to be slowing their carbon uptake much more rapidly than the global average, and some natural GHG sinks may be undergoing processes which will transform them into carbon emitters.
Following a decade of relative stability, for example, the atmospheric concentration of methane (CH4), a potent greenhouse gas, began to rise inexplicably in 2007. Although deteriorating permafrost has been observed in Russia, Sweden, and Tibet, the precise source of the increase has not yet been identified.
As permafrost melts and the depth of its active layer deepens, organic material begins to decay. If the surface is covered with water, methane-producing bacteria break down the organic matter. Such bacteria cannot, however, survive in the presence of oxygen; if thawed soils are exposed to air, carbon dioxide-producing bacteria participate in the decay process. Both events amplify the effects of warming temperatures by releasing greenhouse gases. The likely magnitude of such a positive feedback, which is considered to be a potential tipping element, is unknown.
|Global carbon dioxide emissions from fossil fuel combustion, 1980-2010, as compared to baseline scenarios used by the IPCC to project business as usual emissions. Click to enlarge.|
It is now estimated that if global emission rates could immediately be stabilized at present-day levels, just twenty more years of business-as-usual emissions would give a 25% probability of warming exceeding 2 °C above pre-industrial levels, even if society could achieve zero emissions after 2030.
To stabilize climate, a decarbonized global society-with near-zero emissions of CO2 and other long-lived greenhouse gases-would now have to be reached well within this century in any case. Many of the most up-to-date emissions reduction scenarios require a decline to zero carbon or carbon negative levels by 2050 to limit warming to no more than 2 ºC.
Surface temperatures. Recent global temperatures demonstrate human-induced warming: temperatures have increased at a rate of 0.19 °C per decade for the past quarter century, in close alignment with modeled predictions based on projected greenhouse gas increases. In addition to a warming limit of 2 ºC, many scientists consider an increase of 0.20 ºC per decade to be a “rate of warming” limit beyond which many ecosystems will experience a reduced ability to adapt.
|Annual variability and averaged linear trend of global surface temperatures, 1980-2008. Source: NASA's Goddard Institute for Space Science (GISS) Click to enlarge.|
Although natural, short-term fluctuations are occurring as expected—for example, temperatures were higher in 1998, the record year for temperatures so far, than in 2008—“there is no indication in the data of a slowdown or pause in the human-caused climatic warming trend” that underlies annual or decadal variability.
For example, a La Niña climate pattern was active in 2008. Such a pattern can normally can be expected to reduce average global surface temperatures. At the same time, solar output was at its lowest level of the satellite era, which would normally be expected to create another temporary cooling influence. Absent any anthropogenic warming, these two factors would typically be expected to make 2008 temperatures among the coolest since record-keeping began. However, 2008 was the ninth warmest year on record. “This underpins the strong greenhouse warming that has occurred in the atmosphere over the past century,” write the authors.
|Anthropogenic and solar variability influences on global temperature changes, 1980-2009, and (projected) 2009-2030. Click to enlarge.|
Atmosphere. Worldwide air temperature, humidity and rainfall trend patterns now “exhibit a distinct fingerprint that cannot be explained by phenomena apart from increased atmospheric greenhouse gas concentrations”. Atmospheric temperatures have maintained a strong warming trend since the 1970s (~0.6 °C), consistent with expectations of greenhouse induced warming. Each year of the present decade—2001 through 2008—has been among the top ten warmest years since instrumental records began.
|“The 2007 IPCC Assessment... states clearly that without substantial global reductions of greenhouse gas emissions we can likely expect a world of increasing droughts, floods and species loss, of rising seas and displaced human populations. However, even since the 2007 IPCC Assessment the evidence for dangerous, long-term and potentially irreversible climate change has strengthened.”|
—Met Office, UK, 24 November 2009
This week, the UK’s Met (Meteorological) Office projected that unless an exceptionally cold spell occurs within the next month, global 2009 temperatures will be higher than 2008, making 2009 one of the five warmest years since records began around 150 years ago. 2010 will bring with it the influence of El Niño ocean currents, and the Met office estimates a 50% chance that next year will see record average global temperatures.
Cryosphere. A wide array of satellite-based as well as direct ice measurements “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”; and the contribution of the cryosphere—the portions of the Earth’s surface where water is frozen’to global sea-level has increased from 0.8 millimeters per year in the 1990s to 1.2 millimeters per year today. Many non-polar glaciers are critical sources of drinking water and hydropower.
|Mean modeled Arctic sea-ice area, range of modeled Arctic sea-ice, and observed Arctic sea-ice area, in millions of square kilometers. Click to enlarge.|
In particular, summer-time melting of Arctic sea-ice has accelerated in a manner that no climate model had predicted, with the area of sea-ice melt during 2007, 2008, and 2009 was about 40% greater than the average prediction from IPCC AR4 climate models.
Ice shelves, which connect continental ice sheets to the ocean, are also in flux, with the Antarctic Peninsula seeing 7 major collapses over the past 20 years. Shelf weakening has also been observed in the Bellingshausen and Amundsen seas, indicating a more widespread influence of atmospheric and oceanic warming than previously thought. The collapse of ice shelves often contributes to an accelerated destabilization of ice sheets to which the ice shelves were once attached.
Oceans. Upwards of 80% of the warming created by the emission of manmade greenhouse gases are now stored in the world’s oceans. Satellite data shows recent global average sea level rise (3.4 mm per year over the past 15 years) to be approximately 80% higher than past IPCC predictions. This acceleration is consistent with a doubling in contribution from melting of glaciers, ice caps, and the Greenland and West Antarctic ice sheets.
By 2100, global sea level is likely to rise at least twice as much as the Working Group 1 of the IPCC AR4 had projected just two years ago. If emissions continue to rise unabated, sea level rise may well exceed 1 meter, with an estimated upper limit of around 2 meters sea level rise, by 2100. The relative inertia of oceanic mass ensures that sea levels will continue to rise worldwide for centuries after global temperatures have been stabilized. Several meters of sea level rise must be expected over the next few centuries, regardless of any emissions reductions that may occur during that time.
Ocean acidification and de-oxygenation, both of which are amplified by warming, are also contributing to a decline in the ability of large swaths of the oceans to support marine life. The increase in heat content of the upper ocean between 1963 and 2003 is estimated to be approximately 50% higher than previously estimated, a calculation that is consistent with observed sea level rise during the same period of time.
Resilience. Recent studies suggest that the disruptive effects of climate change may be greater than anticipated at just 2 ºC of warming, and one aspect of climate change that has been particularly difficult to estimate is the ability of a given ecosystem to recover from, or adapt to, a given change in equilibrium.More than a dozen vulnerable tipping elements in the climate system (e.g. continental ice-sheets, Amazon rainforest, West African monsoon, thermohaline ocean circulation cycle) could be pushed towards abrupt and/or irreversible change if warming continues along a business-as-usual trajectory throughout this century. Here, the authors invoke the precautionary principle: waiting for higher levels of scientific certainty could mean that “some tipping points will be crossed before they are recognized.”
At a press conference announcing the release of the report, co-author Richard Somerville of the Scripps Institution of Oceanography in La Jolla, California acknowledged the difficulty of reconciling scientifically documented trends with political goals and media chatter:
There’s an urgency to this that is not political or ideological, but scientific. There are, for example, no liberal or conservative theories of, for example, ocean circulation. There is simply a theory of ocean circulation... A Galileo comes along one every hundred years or so [to successfully challenge science], but most people who think they are Galileo are wrong.—Richard Somerville
I. Allison, N. L. Bindoff, R.A. 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, and A.J. Weaver: The Copenhagen Diagnosis, 2009: Updating The World On The Latest Climate Science. 24 November 2009: The University of New South Wales Climate Change Research Centre (CCRC), Sydney
Met Office: Climate Science Statement, 24 November 2009
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