Climate change has changed
Presented by WWF
Recent observations of ice, atmospheric CO2 and methane, sea level rise and global emissions of greenhouse gases indicate that climate change is impacting natural systems, including the oceans, sooner than predicted in existing modelling and scenarios. Early signs suggest that feedbacks are active now, from marine and coastal environments, which are accelerating climate change and that some tipping points have been passed. Many of these processes are not included in standard climate modelling and predictions. Mitigation efforts are increasingly urgent.
What has changed?
Since the compilation of the most comprehensive and up to date science; the IPCC’s AR4, published in 2007, several aspects of climate science, understanding and observations in the field have advanced.
● The melt of Arctic summer sea ice in summer September 07 and the record amount of thin and young sea ice in the winter of 2008 demonstrate that the Arctic is losing sea ice decades ahead of projections. This triggers feedback mechanisms which accelerate global warming, climate change and impacts further and faster than currently documented. The majority of Arcticsea ice scientists declare that the Arctic sea ice is past its tipping point[i], the point at which change becomes self-perpetuatinguntil an altogether different state is reached. NSIDC suggest that the North Pole may be ice free this summer[ii].
● 2007 saw another high in the growth of atmospheric CO2 in recent years[iii]. This coincides witha reduction of the natural carbon sink capacity of the oceans, for example see[iv].Data show that atmosphericCO2levels are higher than the IPCC worst case scenario, A1F1[v].
● Atmospheric methane concentrations have begun to rise again, after a plateau of 10 years. The source of this methane appears to be fromnorthern wetlands, strongly suggesting that the release of methane from boreal and Arctic soils is accelerating [vi].
● Sea level is rising faster than forecast[vii] and some oceans are acidifying faster than[viii];
● Many of the processes observed and detailed above have the potential to feedback to the climate system, exacerbating and accelerating climate change[ix]. Indications suggest that in some examples, the feedbacks have become active already.
Why does this matter?
The changes in the Arctic matter in particular for two reasons:
i) Speed and causes of impacts. For several key Arctic systems, recently observed changes are happening at rates significantly faster than accommodated for in climate models. This reflects the current limits of scientific understanding of essential processes controlling these Arcticsystems and therefore raisesquestions about the range of predictions that guidemitigation strategies to date.
ii) Potential to cause more positive feedback. The most prominent result from losing Arctic sea ice is a positive feedback to warming through the albedo effect, with potentially dangerous consequences. Further consequences will include warming of Arctic shallow shelf seas and the very real danger of release of methane from shallow shelf seas and coasts. Early evidence suggests that methane is increasingly being released from these sources already.Additionally, the Greenland Ice Sheet could also be impacted by loss of Arctic sea ice, through regional warming. The rate of loss of Greenland Ice Sheet has increased threefold between 2004-2006. It is estimated that if Greenland temperatures rise 3oC above pre-industrial levels, the Greenland ice sheet may pass a tipping point and be committed to complete loss[x]. Loss of Greenland ice has the potential to increase global sea levels by 7.2m over time. NASA’s Hansen recently predicts 3-5m sea level rise by 2100[xi].
How does this fit in with the other climate science ?
Looking at the data in the table below, even big cuts in CO2 emissions carry a serious risk of exceeding 2oC. We have passed the levels of greenhouse gases in the atmosphere which we would need to stabilise at in order to have a chance of staying below 2oC. If we stabilise at current levels, we will likely exceed 2oC. What the Arctic is telling us, is that 2oC is too much. Pacific Islanders echo the same conclusion. It is reported that in the past (Pliocene), when global average temperatures were 2-3oC warmer than now and CO2 was around 385-425ppm, sea levels were 25m higher than now (plus or minus 10m)[xii]. Greenhouse gas levelshave risen above the desired stabilisation target of atmospheric greenhouse gas concentrations, but it is considered that if this is followed by a steep decline in emissions, that it may still be possible to limit temperature rise to below 2oC. However, the modelling clearly demonstrates that any delay, even a few years, in the peak and decline, significantly reduces the possibility to stay even below 2oC.The table below summarises some data releasedpre 2007/8 field observations, so these may be an underestimate.
/ Projected or target globalmean temp
rise since
pre-industrial / Associated
CO2ppm or
Equivalents
Stabilisation level. / Predicted sea level
rise by
2100 in
metres / Peak in
emissions
by given year or since paper published / Associated Reduction in
global CO2
emissions by
2050
Status in 2007 / 0.76oC / 385ppm CO2
430equiv / 17mm/y
IPCC 2007[xiii] / 2-2.4oC in B1, best scenario / 350-400 CO2 / 0.5m / 2000-2015 / 50-85%(or more)
below 2000 levels
IPCC 2007ibid / 0.6-1.4oC / 350equiv
(NASA)
Hansen et al[xiv] / 1.7oC total / 300-350ppm CO2 / 3 to 5m / A few years
(ippr)
Baer and
Mastrandrea[xv] / <=2oC total / 366-380ppm CO2 / 2010 / 81% below 1990 = 9-26% risk of exceeding 2oC
Meinshausen[xvi] / 2oC total / Risk of overshooting 2oC
350equiv=0-31%(mean 8%)
400equiv =2-57%(mean 27%) / For 400ppm CO2 e model,
2-5y from ‘06 / 30-40% below
1990 levels
Parry et al.[xvii] / 2oC / 400-470ppm CO2equiv / 80% below 1990
When the predictions for emissions targets and temperature increase targets are combined with the new field observations from 2007 and 2008, it becomes clear that the system seems to be reacting faster and more sensitively than predicted. The modelling and predictions need to be updated and the mitigations targets established on the basis of these re-calculated data.
Conclusions
This new information indicates that many aspects of climate change have been underestimated; the impacts are felt sooner, the feedbacks are active sooner, the climate is more sensitive than anticipated and the models used for IPCC 4th AR have failed to accurately predict the pace of change.While it is already considered a challenge to limit global average temperature rise to below 2oC, given the impacts underway, the feedbacks in action and tipping points, it is now highly likely that a rise of 2oC would be too much. The aim of UNFCCC is to avoid “dangerous interference with the climate system”; the changes now underway and the feedbacks in action indicate that we may have already reached ‘dangerous’ levels of climate change. The implication of this recent evidence is that our mitigation and adaptation responses to climate change now need to be more rapidly implemented and greater than previously assessed.
1
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[ii] National Snow and Ice Data Centre, 2008.
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[x] ACIA, 2005. Arctic Climate Impact Assessment, Cambridge, CambridgeUniversity Press.
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[xiii] Solomon, S., et al., 2007: Technical Summary. In: Climate Change, 2007: The Physical Basis. Contribution to Working Group I to the Fourth Assessment Report of the IPCC. CambridgeUniversityPress, UK and USA.
[xiv] Hansen, J., Sato, M., Pushker, K, Beerling, D., Masson-Delmotte, V., Pagani, M., Raymo, M., Royer, D. and Zachos, J. 2008. Target Atmospheric CO2: Where Should Humanity Aim?. Pp1-38.
[xv] Baer, P. and Mastrandrea, M. 2006. High Stakes: Designing emissions pathways to reduce the risk of dangerous climate change. ippr. Pp 1-37.
[xvi] Meinshausen, M. 2006. What Does a 2°C Target Mean for Greenhouse Gas Concentrations? In Avoiding Dangerous Climate Change, Editor, Schellnhuber. Camb Uni Press. Pp 1-406.
[xvii] Parry, M., Palutikof, J., Hanson, C., Lowe, J. 2008. Climate Policy: Squaring up to Reality. Nature Reviews, Climate Change. 29th May 2008.