The effects of global warming and climate change
Introduction
Global climate change is now widely recognised as one of the foremost – perhaps the foremost – environmental challenge of the 21st century. The evidence for human influence on climate change through emissions of
greenhouse gases (mainly carbon dioxide from fossil fuel burning, and methane from various sources), is now very strong. Climate change has importance for health in two main ways. First, some degree of climate change now appears
inevitable, which means it is necessary to learn to adapt to climate change and to consider how to protect the population against its adverse effects. Those adverse effects include direct effects of extreme weather, changes in the
frequency, distribution or burden of ‘climate-sensitive‘ diseases, and indirect effects operating through such mechanisms as changes to crop production and water availability. At the same time, major changes are needed in all sections of
the economy to try to reduce human influence on climate change through reduction of greenhouse gas emissions (mitigation). This implies substantial changes in energy use, transportation and in other sectors, which themselves are likely to have
effects on health, for example through reduction of toxic air pollutants if dependence on the burning of fossil fuels is reduced.
Key definitions and terms
| Adaptation | Strategies, policies and measures undertaken now and in the future to reduce potential adverse impacts of climate change. |
| Climate | The average state of the atmosphere and the underlying land or water in a specific region over a specified time scale. Should be distinguished from weather, which is the atmospheric conditions at a specific place and time. |
| Climate change | A statistically significant variation in either the mean state of the climate or in its measurable variability, persisting for an extended period (typically decades or longer). |
| Greenhouse Gases (GHGs) | Gases present in the Earth's atmosphere which reduce the loss of heat into space and therefore contribute to global temperatures through the greenhouse effect. |
| IPCC | Intergovernmental Panel on Climate Change, an international body of scientists tasked with evaluating the risk of climate change caused by human activity. It was established in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP), two organizations of the United Nations. |
| Mitigation | An anthropogenic (human) intervention to reduce the sources or enhance the sinks of greenhouse gases. |
Climate change
| Climate and climate in context | Climate change has been a constant feature throughout the history of the Earth. Over different timescales, these changes have been driven by a variety of natural processes, among them plate tectonics, volcanic eruptions, changes in the ocean-atmosphere circulation, variations in the orbit of the Earth and in its obliquity and precession of spin (the main factors responsible for the glacial cycles of the last half million years or so), and variations in solar output. Life itself has played a crucial role through its acceleration of rock weathering and in the capture of carbon in plant biomass and marine sediments which are central to the long-term carbon cycle. |
| Anthropogenic climate change | There is now recognition that human activity is contributing to changes in the composition of the atmosphere which are likely to lead to climate change over this century. The main focus is on carbon dioxide generated by the burning of fossil fuels, but other greenhouse gases (GHGs) include:
Thus land use changes, agriculture and many other aspects of human activity contribute to global warming. |
| Rapidity of climate change | There is nothing ‘optimal’ about the current climate. The Earth has been much warmer (and cooler) than now and, over geological timescales, climate change is the norm and occasionally abrupt. However, over the last 10,000 years (the Holocene), the climate has been unusually stable. This stability may have been an important factor in the development of agriculture and the flourishing of human civilization. Concerns about climate change over this century relate to:
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| IPCC scenarios | It is not possible to be precise about the course of climate change, but scenario-based modelling carried out for the IPCC suggest increases in global mean temperatures which are rapid and large in magnitude. The range of scenario estimates published in the most recent (fourth) IPCC report suggest several degrees Celsius warming is likely compared with around a 5 degree Celsius increase in temperatures since the depth of the last glacial maximum around 18,000 years ago. Such change is likely to disrupt natural ecosystems upon which we all depend, as well as being a direct threat to human populations. |
Effects on health
| Among the many effects of climate change are likely to be direct and indirect effects on health (figure), including: | |
| Direct effects |
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| Indirect effects |
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| The most predictable impacts on health may not be the most important. There is much uncertainty about the potential effects of rapid climate change on ecosystems already under pressure from human activity. The regional impacts are particularly difficult to predict. Local changes in precipitation and temperature may make unsustainable some forms of habitation for humans and other species, and the impacts may follow a non-linear trajectory. Effects on agriculture and water resources may be among the most important (malnutrition, environmental migrations, economic impact). |
Responses
| Adaptation |
Some degree of climate change is now inevitable because the principal greenhouse gas, carbon dioxide, remains in the atmosphere for many decades: the current levels are sufficient to increase temperatures, and climate modelling indicates It is therefore important for populations to learn to adapt to climate change. Adaptation strategies may include:
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| Mitigation | At the same time, there is recognition that it is important to try to limit the degree of climate change by reducing greenhouse gas emissions and other measures. There are formidable social, political and technological barriers to achieving the changes on the required scale and speed, but there is also increasing recognition that many of the changes are likely to have substantial net benefits to health, because of such factors as reduction in outdoor air pollution. |
Key references
- World Health Organization. Climate Change and Human Health - Risks and Responses. Summary. Geneva: WHO, 2003. (Available as pdf on-line: http://www.who.int/globalchange/climate/en/ccSCREEN.pdf)
- Patz JA, Campbell-Lendrum D, Holloway T, Foley JA. Impact of regional climate change on human health. Nature. 2005 Nov 17;438(7066):310-7
- Haines A, Kovats RS, Campbell-Lendrum D, Corvalan C. Climate change and human health: impacts, vulnerability, and mitigation. Lancet. 2006 Jun 24;367(9528):2101-9
Useful websites
- The Intergovernmental Panel on Climate Change
http://www.ipcc.ch/ - The World Health Organization website on Climate change and human health
http://www.who.int/globalchange/climate/en/
© Dr Paul Wilkinson 2009
