Environment Watch shares with you this month the conclusion of the article published two weeks ago on the environmental education page Our Habitat in the Career & Education publication.

THERE is consensus on the need for co-ordinated action to advance the goal of a low-carbon economy and adaptation to climate change, and with all deliberate speed.

This week we elaborate on the basic process of the sciences for a better understanding of the climate change debate.

The Intergovernmental Panel on Climate Change

Climate scientists have worked independently or collectively on various aspects of the process for over 20 years. The process has been facilitated by the formation of the Intergovernmental Panel on Climate Change (IPCC) in 1988, by the World Meteorological Organisation and the United Nations Environment Programme to assess “the scientific, technical and socio-economic information relevant for the understanding of the risk of human-induced climate change”.

The IPCC has so far conducted four assessments in 1990, 1995, 2001 and 2007, the latter being referred to as AR4. The next assessment is underway and due in 2013.

The detection process and findings of the IPCC

One of us participated actively in this process and can attest to the high degree of confidence in the findings and the soundness of the methodologies.

The IPCC started with collection of past data, mainly instrumental data over the last century and a half, but also proxy data, especially for periods when instrumental records were not available. For example, changes in tree rings have been used as proxy data to determine the lengths of past growing seasons, and hence of temperatures. In addition, pockets of air, captured and encapsulated in ice and covered over by new snow and ice thousands of years ago, are retrieved by drilling out ice cores and analysed to determine the character of the atmosphere, such as its concentration of carbon dioxide, thousands of years ago.

All data are critically analysed, especially statistically, and subjected to peer review before publication. Based on these analyses, AR4 has been able to conclude:

* that “the total (global) temperature increase from 1850-1899 to 2001-2005 is 0.76°C ± 0.19°C”; and

* that “the concentration of atmospheric CO2 has increased from a pre-industrial value of about 280 ppm (parts per million by) to 379 ppm in 2005”.

As atmospheric CO2 concentration was found to increase by only 20 ppm over the 8,000 years prior to industrialisation, it is natural to conclude that the quantum leap was due to industrialisation, mainly from the burning of fossil fuel.

Attributing the cause of temperature rise is much more complex than the analysis of data. Firstly, all possible causes of temperature changes, both natural and man-made, are investigated using controls to isolate causes.

Of particular importance are natural changes in solar radiation which affects the amount of heat reaching the earth; increases in greenhouse gases, such as carbon dioxide and methane, which cause the temperature of the earth to increase due to the trapping of radiation from the earth; and changes in the number of aerosols or minute particulates in the atmosphere which can affect the amount of solar radiation reaching the earth, most times producing cooling.

The effects of these changes on the net radiation reaching the earth, incoming minus outgoing, are studied and expressed in units of Watt per square metre (W m-2).

Considering the man-made contribution to the changes in radiation levels, AR4 concluded that “the understanding of anthropogenic warming and cooling influences on climate has improved (since the 3rd assessment), leading to very high confidence that the effect of human activities since 1750 has been a net positive forcing (leading to warming) of +1.6 W m-2”.

By comparison, the contribution to warming by changes in solar radiation only is 0.12 W m-2.

Secondly, it needs to be demonstrated that both natural variability and man-made forcing can adequately explain the observed changes in temperature. This was done by the use of General Circulation Climate Models run on super computers.

These models are dynamic in nature, as opposed to statistical models, and include equations representing the physics and chemistry of the atmosphere and the atmospheric interaction with vegetation, land and ocean. Given some initial atmospheric conditions, usually observed data, the equations are computed (solved) and stepped forward in time so that the models keep generating climate information once the initial conditions are given.

Thus the climate over a period of time is generated by computer models, which themselves are validated by comparison with observed data. This is done by feeding the model some initial conditions based on past data and allowing the model to generate climate over a known period for which observed data are available for comparison.

Once a model has been validated, numerical experiments using different initial conditions and climate composition are computed. One of the most striking experiments done for AR4 was to demonstrate that several independent models driven by both known natural and man-made forcing (solar radiation, naturally occurring greenhouse gases, man-made greenhouse gases and aerosols) could describe the observed decadal averaged temperatures over the period from 1906 to 2005, whereas the models driven only by natural forcing (solar radiation and naturally occurring greenhouse gases) grossly underestimated the observed temperatures during the period.

These experiments were done for both globally averaged temperatures and for temperatures averaged over the regions of the globe.

Future Scenario

Based on expanded numerical experiments, AR4 concluded that “continued greenhouse gas emissions at or above current rates would cause further warming and induce many changes in the global climate system during the 21st century that would very likely be larger than those observed during the 20th century”.

Climate science has its limitations, mainly uncertainties in the degree of confidence in climate model results. To limit the uncertainty, the results from many models are averaged. Techniques of averaging give consensus values and measures of deviation from the consensus so that users of model results know the extent of the uncertainties with which they are working.

As the science continues to improve and evolve, the uncertainties become less. The most recent paleo-climatology studies indicate that a rise in temperature of 2ûC above pre-industrial values may cause changes in the climate system from which it is not likely to reverse itself, such as the melting of the polar ice caps.

Sea level rise would be one major consequence with existential threats to large segments of the earth’s population.

Jamaicans in concert with other island coastal communities will need to be more attentive and proactive.

Professor A Anthony Chen is Professor Emeritus of Applied Atmospheric Physics at the UWI and Climate Studies Group, Mona.

K G Anthony Hill is a Jamaican Ambassador (retired) and convenor of the Reflexion Group, a non-governmental organisation on international affairs.