Evidence of Human Generated Climate Change

The release on 13 February 2010 of a briefing note acknowledging a lack of clarity in reporting background data by the Intergovernmental Panel on Climate Change combined with the events surrounding the publishing of emails from the University of East Anglia have furthered the public misapprehension that a scientific consensus does not exist in favour of climate change. A recent poll{1} found that four-fifths of people are unaware of the consensus or rejected it.

Behind the occasional high profile challenge there is extensive evidence on the three issues of climate change: Is climate change actually occurring? Are humans responsible for the change? Is climate change a bad thing?

Is climate change actually occurring?

Some critics of climate change suggest that the earth’s temperature is actually an oscillation in temperature within normal limits and that the temperature will drop again.

However – whilst climate models differ in their predictions of the extent of future change – even the most conservative models predict in excess of 1C rise in temperature{2}; a proportionally large increase.

Evidence of past events paints a starker picture. The US Global Change Research Program found extensive evidence of a rise in temperature including “… average winter temperatures in the Midwest and northern Great Plains increasing more than 7F(3.9C)….”{3}. The report concludes that some changes are occurring faster than previous models predicted.

The Centre for Hydrology and Ecology has reported that the lifecycles of some species have moved up to 11 days. Dr Stephen Thackeray believes this to almost certainly be caused by climate change {4}.

The scientific community across the world accept climate change as a fact, as is shown by the joint statement of national scientific organisations bodies of Brazil, China, India and all G8 nations{5}.

Are humans responsible for the change?

Whilst changes in climate do occur naturally, they are due to an external influence. At a most basic level this can be a change in the atmosphere, a change in the heat of the Sun, or a change in the orbit of the Earth.

The orbit of the earth has changed over the course of tens of thousands of years, so can be discarded as a cause of the significant changes since the start of the Twentieth Century.

Previous periods of climate change have been linked to changes in solar luminosity. However, scientific studies{6} show that current variations are not significant.

Clearly current changes are caused by changes in atmospheric composition.

Some critics claim this change is natural and not human generated pointing to the fact that over 95% of atmospheric CO2 is from nature not man; for instance, termites produce CO2 emissions many times that of global industry and vehicle use combined{7}.

However, the change in CO2 emissions fully supports a human source. Studies of the type of Carbon in atmospheric and absorbed CO2{8}{9} show that the ratio of natural CO2 to CO2 from combustion of fossil fuels is at the lowest it has been in 10,000 years. The studies pinpoint the start of this decline to the middle of the Nineteenth Century.

This change – whilst small in comparison to the proportions of CO2 to other gases – is large in comparison to natural variation in CO2 levels.

The majority of change in CO2 levels not attributable to burning of fossil fuels appears to arise from deforestation{10}.

Overall the increase in CO2 concentrations since the Industrial Revolution has been 36%{11}.

Currently a proportion of CO2 emissions absorbed by plants and the oceans, dampening the effects of increased emissions. However, studies{12} suggest that these carbon sinks might be exhausted as early as the middle of the Twenty-First Century. Any atmospheric effect of CO2 would then accelerate.

The increase in CO2 alone makes human impact visible. The evidence becomes even clearer when considering methane levels. Atmospheric Methane has risen 148% since the Industrial Revolution{11}. This variation in levels is due to human industry and agriculture{13}.

As well as the direct effect increases in human generated greenhouse gases increases natural release of greenhouse gases.

One example of this is ice albedo. Increases in greenhouse gasses produce an increase in temperature, causing a decrease in polar ice. This leads to (i) increased surface area of seawater and (ii) decreased reflection of solar heat. As evaporation is proportional to surface area and to the amount of heat not reflected, the amount of water vapour is increased by two factors. As water vapour has a significant impact the small change in atmospheric composition cascades into a significant change overall.

A few critics suggest that in prehistory the level of greenhouse gases has been higher than currently without the temperature be higher; this ignores differences in solar luminosity and orbital patterns.

Is climate change a bad thing?

A small group of critics, amongst them Professor Siegfried Frederick Singer, accept that human generated climate change is occurring but welcome it as increasing the growing season, and consequent economic benefits.

This only applies if temperatures rise less than 2C and only benefits some parts of the developed world{14}, and is the only theoretical benefit.

Melting of the icecaps, combined with the thermal expansion of seawater will produce a rise in sea levels.

Over 20% of the world’s population live within 30 km of a shoreline, so will be directly impacted. One stark example is that 80% Maldives less than 1 meter above sea level{15}.

A conservative analysis based on NASA scans can be found here{16}.

As well as the flooding of land, increased sea levels will increase coastal erosion and push wetlands back reducing the quality of remaining coastal areas{18}.

Further, salt water will contaminate ground water leading to degradation of drinking water and irrigation. Thailand, Israel, China, Vietnam and some island states are already experiencing this {18}.

Studies{2} have also found an increase in heavy downpours, which threaten the 70% of the world’s population live on a flood plain{15}.

Medical studies show that increased temperatures will have a direct effect on health in the form of increased thermal stress, and greater spread of infectious diseases{17}.

As the majority of road and rail connections follow valleys access to medical care will also be severely impacted by loss of infrastructure.

So, whilst a few areas of land that are, not too dry and not too wet, not too high and not too low, might see an economic benefit if a slight change in climate occurs they will be the luck few, and will certainly not have a flourishing global market upon which to trade their benefits.


So – whilst we must continue with a strong debate on all aspects of climate change – that discussion must be on the evidence. And stripped of politics and character attacks, the evidence overwhelmingly shows human activity as an accelerant of negative climate change.

{1} On 3 December 2009, the World Bank published Public attitudes toward climate change: findings from a multi-country poll.
{2} 2007 IPCC Report
{3} US Global Change Research Program Global Climate Change Impacts in the United States (June, 2009)
{4} Radio 4 Today programme 9 February 2010 http://news.bbc.co.uk/today/hi/today/newsid_8505000/8505517.stm
{5} Joint science academies’ statement: Global response to climate change 7 June 2005
{6} Hansen, J. “Climate“. Journal of Geophysical Research (2002) and “Efficacy of climate forcings” Journal of Geophysical Research (2005)
{7} (Science, 5 November 1982).
{8} Stuiver, M., et al. (1984) 13C/12C ratios and the transfer of biospheric carbon to the atmosphere J. Geophys. Res. 89, 1731-1748, and Francey, R.J. et al. (1999) A 1000-year high precision record of d 13Cin atmospheric CO. Tellus 51B, 170 193.
{9} Bahm, F., et al. (2003), Evidence for preindustrial variations in the marine surface water carbonate system from coralline sponges Geochem. Geophys. Geosystems, 3/3, DOI 10.1029/2001GC000264
{10} IPCC (2001). Summary for Policymakers. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change
{11} EPA (2008). Recent Climate Change: Atmosphere Changes Climate Change Science Program
{12} Cramer, W Future trajectories of global terrestrial carbon fluxes
{13} P. Bousquet et al. Contribution of anthropogenic and natural sources to atmospheric methane variability Nature 443, (28 September 2006)
{14} Smith, J.B., et al. (2001). Chapter 19: Vulnerability to Climate Change and Reasons for Concern: A Synthesis in Hope C. and Sinha S.K. (eds.) and Climate Change 2001: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, United Kingdom: Cambridge University Press
{15} UNFCCC (2005) Climate Change, Small Island Developing States. http://unfccc.int/resource/docs/publications/cc_sids.pdf
{16} http://flood.firetree.net/
{17} McMichael AJ, et al. (2006). “Climate change and human health: present and future risks“. Lancet 367 (9513): 859–69
{18} SURVAS http://www.survas.mdx.ac.uk/content.htm

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