Climate change is one of the most serious environmental threats facing the world. Its impacts are likely to be felt globally as temperatures increase, sea levels rise and patterns of drought and flooding change.
Rising temperatures
The average temperature of the atmosphere near the Earth’s surface has risen by about 0.75°C since around 1900. Even if all greenhouse gas emissions were to stop now, the world is already ‘committed‘ to around 0.6 (+/- 0.3)°C of further warming. If no action is taken to reduce emissions, temperatures will rise even further.
Depending on the future levels of greenhouse gas emissions, increases in global average temperatures may be between 1.1 and 6.4°C from 1990 levels by the end of this century. Temperature changes will not be uniform over the globe. High latitudes, particularly the Arctic, are likely to have larger temperature increases.
Rising sea levels
Globally the average sea level could rise by 18 to 59 centimetres, or more, by the end of the century. However, sea level is not rising uniformly around the world. In some regions, rates are up to several times the global mean rise, while in other regions sea level is falling.
Low-lying areas and many small island states are particularly vulnerable to sea-level rise. Millions of people living in these regions could be put at greater risk of flooding and some small islands could even become uninhabitable.
Extreme weather
Globally, continued warming means extreme weather events are likely to become worse. Heat waves and heavy precipitation are likely to become more frequent throughout this century. Droughts may also become more intense in some regions.
The impacts of these changes are likely to be worst in developing countries. These countries are often the most vulnerable and have the lowest capacity to adapt to a changing climate.
Plants and animals
Changes in rainfall and temperature will likely affect many animal and plant species around the world. Some species might be unable to adapt or move quickly enough to areas with suitable climates, and habitats might not be available for them to move into.
Under high levels of climate change, large areas of the Amazon rainforest could be lost due to drought or uncontrolled spread of fire. The level of impact depends largely on how patterns of rainfall will change over the region. Some projections show major drying and therefore an increased risk of rainforest loss.
Ocean acidification
Over time as atmospheric CO2 concentrations increase, the ocean will become more acidic. This will have potentially profound, but as yet unclear, impacts on marine life. Many marine organisms make shells and plates out of calcium carbonate. This process of ‘calcification’ is important to their biology, and survival is made more difficult as the water becomes more acidic.
Food and water
The exact impacts on crops will vary by region and crop type, and will depend on changing patterns of precipitation and extreme events. The IPCC’s 2007 report summarised that globally, food production could increase with local average temperature rises between 1 to 3 °C above pre-industrial levels. Above this, yields of all major cereal crops in all the main areas of production were projected to decrease. This would result in an increased risk of hunger and malnutrition in the poorest regions of the world.
Water availability for irrigation and drinking will be less predictable because rain is likely to be more variable and higher temperatures could lead to an increased frequency of droughts. It is also possible salt water from rising sea levels may contaminate underground fresh water supplies and soils in coastal areas, affecting drinking water and the ability to grow crops in these areas.
Health
Climate change could have serious consequences for the health of millions of people, particularly those with low ability to adapt to climate change, through:
- increases in malnutrition and consequent disorders, with implications for child growth and development
- increased deaths, disease and injury due to heatwaves, floods, storms, fires and droughts
- altered spatial distribution of some infectious disease vectors
The costs of climate change
The costs of climate change could be huge, as the Stern Report on the economics of climate change made clear. The report estimated that not taking action could cost from 5 to 20% of global gross domestic product (GDP) every year. In comparison, reducing emissions to avoid the worst impacts of climate change could cost around 1% of global GDP each year. Costs will of course depend on the ability of nations to adapt and on the level of future greenhouse gas emissions.
Wider risks
Several recent scientific reports have highlighted the possibility of abrupt climate change: an accelerated change or abrupt shift in the climate system as a result of human interference with the climate system.
As temperatures rise, the risks of such events become higher – including:
- possible slowdown of the North Atlantic ocean thermohaline circulation
- changes in the carbon cycle
- further, rapid loss of sea ice
- further melting of glaciers and the Greenland and West Antarctic ice sheets, leading to long-term and irreversible sea level rise
Although there are substantial uncertainties about these changes, the risks may become significant for global temperatures 2 to 3˚C or more above pre-industrial levels.