A Note on the Latest Science

4th March 2008

This note is compiled from a review of online resources published by James Hansen, David Wasdell, the Tyndall Centre, the Hadley Centre, the IPCC and the Royal Society.

Latest Evidence¹

• 2007 tied with 1998 as the second warmest period on record, after the warmest year yet, 2005. The unusual warmth of 2007 is notable because natural processes, including solar irradiance and the El Nino-La Nina cycle, would indicate a cooling of average temperature.

• Record low sea ice cover in the Artic occurred in September 2007.

• It is unlikely, according to James Hansen, that there will be any readjustment in line with the cooling effect of natural processes in 2008, as underlying warming is expected to continue. Indeed Hansen suggests that, barring the unlikely event of a large volcanic eruption, a record global temperature exceeding that of 2005 can be expected within the next 2-3 years because when the next El Nino occurs it is likely to carry global temperature to a significantly higher level than in recent centuries.

Tipping Elements in the Earth's Climate System²

A paper of this title involving scientists from the Tyndall Centre, the Potsdam Institute for Climate Impact Research, Environmental Change Institute at Oxford, Carnegie Mellon University and Harvard University, was published in February 2008, It followed a workshop which brought together 36 experts and 52 other members of the international scientific community.

The paper describes 'tipping elements', sub-systems of the earth's climate which are at risk of passing a tipping point within the next century. The Term 'tipping point' means a critical threshold at which a small change in human activity can have large long-term consequences.

Below is a map of the potential tipping elements in the climate system which were identified. The sub-systems indicated could pass a threshold (beyond which it would be impossible to restore equilibrium) this century in response to human-induced climate change.

The focus on these tipping elements comes about because they are primarily influenced by human activity, are important for human welfare, and also because whether or not the critical threshold is reached in each case could depend upon today's policy choices, ie: with the right political action now, the trigger for long-term adverse change could be averted.

From the total number considered, and shown on the map, the authors derived a shortlist of nine. The following table describes the time it would take for each sub-system to undergo a major transition once the tipping point was passed, and the key impacts of each major transition.

The authors conclude that the greatest threats, because of their sensitivity to global warming and the certainty with which the physical responses is understood, are tipping the Arctic sea-ice and the Greenland ice-sheet. The authors note that policy analysis and implementation will be extremely challenging because the impacts of climate change are not always predictable or 'linear'. In addition, policy-makers will need to take account of intergenerational justice issues and interpersonal equity over the long-term and with uncertain conditions. Interestingly they point to the need for a rigorous study of potential tipping elements in human socioeconomic systems, ie: to address whether and how a rapid societal transition towards sustainability could be triggered.

Averting the Danger³

• In a paper co-authored by James Hansen, the authors note that the best chance for averting ice sheet disintegration involves a combination of intense reduction in CO2 and other GHG emissions. They note, however, that even then, it is probable that a dangerous level of GHG concentration will be surpassed, even if only temporarily. The dangerous level of CO2 concentration is considered somewhat lower than 450 ppm because of feedbacks, "The evidence indicates we've aimed too high -- that the safe upper limit for atmospheric CO2 is no more than 350 ppm," James Hansen said in December 2007⁴, and he claims we are already at 383 ppm.

• They say that even if we have not already gone past the dangerous threshold, the energy infrastructure we have in place ensures that we will surpass it within a few decades at best.

• In conclusion, the authors of this paper recommend that a feasible strategy for planetary rescue almost certainly requires a means for extracting GHGs from the atmosphere.

Implications for Operation Noah

If scientists consider that we may already have passed the dangerous level of GHG concentration in the atmosphere, then clearly we need to aim to come back within it as soon as possible to prevent further warming and initiate the possibility for planetary cooling. To do this, according to James Hansen and others, we need a combination of ceasing to emit GHGs and removing GHGs from the atmosphere in large quantities, if that is possible.

In light of this, we might reasonably consider that the aim for humanity should be a reduction in GHG emissions to zero, today. In terms of the science, therefore, ON's ask for a 90% reduction by 2030 looks conservative, not radical.