• The main impacts of climate change will be due to sea level rise, increases in temperature and heat waves and a more intense hydrological cycle leading on average to more frequent and intense floods, droughts and storms (see Table 7.6 for a summary of impacts of extreme events).

• There are many ways in which the environment is being degraded due to human activities, for instance, through over-withdrawal of ground-water, loss of soil or deforestation. Global warming will exacerbate these degradations.

• To respond to climate change impacts, it will be necessary to adapt. In many cases this will involve changes in infrastructure, for instance new sea defences or water supplies. Many of the impacts of climate change will be adverse, but even when the impacts in the long term turn out to be beneficial, in the short term the process of adaptation will mostly have a negative impact and involve cost.

• Through adaptation to different crops and practices, first indications are that the total of world food production may not be seriously affected by climate change - although studies have not yet taken into account the likely occurrence of climate extremes. However, the combination of population growth and climate change will mean that disparity in per capita food supplies between the developed and the developing world will become much larger.

• Because of the likely rate of climate change, there will also be a serious impact on natural ecosystems, especially at mid to high latitudes. Forests especially will be affected by increased climate stress causing substantial dieback and loss of production, associated with which there is the positive feedback of additional carbon dioxide emissions. In a warmer world longer periods of heat stress will have an effect on human health; warmer temperatures will also encourage the spread of certain tropical diseases, such as malaria, to new areas.

• Economists have attempted to estimate the average annual cost in monetary terms of the impacts that would arise under the climate change due to a doubling of pre-industrial atmospheric carbon dioxide concentration. If allowance is added for the impact of extreme events, the estimates are typically around 1% to 4% of GDP for developed countries and 5-10 % or more for many developing countries. Later chapters will compare them with the cost of taking action to slow the onset of global warming or reduce its overall magnitude. However, these attempts at monetary costing only represent a part of the overall impact story that must include the cost in human terms, for instance, the large social and political disruption some of the impacts will bring. In particular, it is estimated that there could be up to 3 million new environmental refugees each year or over 150 million by the middle of the twenty-first century. Refinements of all these estimates and the assumptions on which they are based are urgently required.

• Estimates of overall impact need to take the longer term into account. The cost of continuing with business-as-usual (BAU) has been estimated by the Stern Review as the equivalent of 5-20% reduction in per capita consumption now and for ever with a strong likelihood that it will be in the upper part of that range and with disproportionate losses falling on poorer countries.

However, many will ask why we should be concerned about the state of the Earth so far ahead in the future. Can we not leave it to be looked after by future generations? The next chapter will give something of my personal motivation for caring about what happens to the Earth in the future as well as now.

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