Introduction of climate change
Human activities are releasing greenhouse gases into the atmosphere.
Carbon dioxide is produced when fossil fuels are used to generate energy and when forests are cut down and burned. Methane and nitrous oxide are emitted from agricultural activities, changes in land use, and other sources. Artificial chemicals called halocarbons (CFCs, HFCs, PFCs) and other long-lived gases such as sulphur hexafluoride (SF6) are released by industrial processes. Ozone in the lower atmosphere is generated indirectly by ,amongst other things, automobile exhaust fumes and other sources.
Rising levels of greenhouse gases are already changing the climate.
By absorbing infrared radiation, these gases control the way natural energy flows through the climate system. In response to humanity's emissions, the climate has started to adjust to a "thicker blanket" of greenhouse gases in order to maintain the balance between energy arriving from the sun and energy escaping back into space. Observations show that global temperatures have risen by about 0.6 ˚C over the 20 th century. There is new and stronger evidence that most of the observed warming over the last 50 years is attributable to human activities.
Climate models predict that the global temperature will rise by about 1.4 – 5.8°C by the year 2100.
This change would be much larger than any climate change experienced over at least the last 10,000 years. The projection is based on a wide range of assumptions about the main forces driving future emissions (such as population growth and technological change) but does not reflect any efforts to control emissions due to concerns about climate change. It is based on current emissions trends and assumes that no efforts are made to limit greenhouse gas emissions. There are many uncertainties about the scale and impacts of climate change, particularly at the regional level. Because of the delaying effect of the oceans, surface temperatures do not respond immediately to greenhouse gas emissions, so climate change will continue for hundreds of years many decades after atmospheric concentrations have stabilized. Meanwhile, there is new and stronger evidence that most of the warming observed over the last 50 years can be attributed to human activities.
Human society will face new risks and pressures.
Food security is unlikely to be threatened at the global level, but some regions are likely to experience food shortages and hunger. Water resources will be affected as precipitation and evaporation patterns change around the world. Physical infrastructure will be damaged, particularly by sea-level rise and by extreme weather events. Economic activities, human settlements, and human health will experience many direct and indirect effects. The poor and disadvantaged are the most vulnerable to the negative consequences of climate change.
In this summary we look first at the possible biophysical responses of agro ecosystems to the specific environmental changes that are anticipated as a result of the buildup of global greenhouse gases, and then at the range of adaptive actions that might be taken to ameliorate their effects. It’s including discussions of regional and global assessments, the effects of uncertainty, thresholds, and surprises, and the possible consequences of global warming on agricultural sustainability and food security.