The effects of global warming and climate change

The effects of global warming and climate change



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


Strategies, policies and measures undertaken now and in the future to reduce potential adverse impacts of climate change.


The average state of the atmosphere and the underlying land or water in a specific region over a specified time scale (usually longer term).  Should be distinguished from weather, which is the atmospheric conditions at a specific place and time, usually the day to day variations.

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.


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 Organisation (WMO) and the United Nations Environment Programme (UNEP), two organisations of the United Nations.


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:

  • methane;
  • nitrous oxide;
  • ozone;
  • chlorofluorocarbons (CFCs).

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 civilisation.  Concerns about climate change over this century relate to:

  • the expected pace of change;
  • our dependence on intense utilisation of the Earth's resources;
  • population density.

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 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

  • Health impacts of temperature extremes, specifically of heat waves. In the UK, for example, under credible climate change scenarios, the type of heat wave seen in Paris in 2003[1] and Europe in 2006 is likely to become a once-in-two-year event by around the middle of this century.
  • Increased frequency of extreme weather events, including severe storms, floods and droughts.
  • Sea level rise which will threaten many low-lying areas with inundation.
  • Increased frequency of food- and water-borne diseases.
  • Potential for change in the seasonal patterns or geographical distribution of some vector-borne disease.
  • Interactions with air pollution and effects on the seasonality and duration of aeroallergens.

Indirect effects

  • Impacts on water resources and agricultural productivity – with potential for socio-economic dislocation and mass migration of environmental refugees.

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).





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 that the increases will begin to become appreciable in the fourth and fifth decades of the century.

It is therefore important for populations to learn to adapt to climate change.  Adaptation strategies may include:

  • infrastructure developments, including specific protection measures (e.g. against heat or flood risks, and solar shading).
  • public health protection measures (e.g. heat-health warning systems, vaccinations for vector borne diseases).
  • information dissemination.


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, increased crop growing seasons, warmer climates.

Latest developments

The Paris UN Climate Change Agreement: on 22 April 2016 –  175 world leaders signed the Paris Agreement at the United Nations Headquarters. Adopted in Paris by the 196 parties to the UN Framework Convention on Climate Change (UNFCCC) at a conference known as (COP21), the Agreement’s objective is to limit global temperature rise to well below 2 degrees Celsius, and to strive for 1.5 degrees Celsius. At least 55 countries, accounting for 55 per cent of global greenhouse gas emissions, deposit their instruments of ratification[2].

The UK Climate Change Act 2008[3] requires the net UK carbon account for all six Kyoto greenhouse gases for the year 2050 is at least 80% lower than the 1990 baseline, towards actions avoiding dangerous climate change, and a 35% reduction by 2020 for the UK. The Act promotes the UK to become a low-carbon economy and gives ministers powers to introduce the measures necessary to achieve a range of greenhouse gas reduction targets. An independent Committee on Climate Change was created under the Act to provide advice to Government on these targets and related policies[4].



Key references

  • World Health Organisation.  Climate Change and Human Health - Risks and Responses.  Summary.  Geneva: WHO, 2003.  (Available as pdf on-line:
  • 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


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  © Dr Paul Wilkinson 2009, Rebecca Close and Helen Crabbe 2016