evidence that the Earth's climate has demonstrably warmed since the pre-industrial era and that most of the warming over the last 50 years is very likely to have been due to increases in greenhouse gas13 concentrations in the atmo­sphere. Atmospheric concentrations of these gases are at their highest recorded levels and continue to go up, mainly due to combustion of fossil fuels, agriculture and land-use change (Figure 5-3). It is generally not the changes in the means of weather variables that impose the greatest risks, but the increase in frequency or intensity of extreme events that pose challenges to agricultural systems. The full ap­pearance of many of the impacts of these changes is delayed by inertia in the climate system and in the behavior of eco­systems (IPCC, 2007ab).
     Agricultural climate change response options are often taken in the context of other stresses and objectives through a range of technological, behavioral and policy changes. While the impacts of a changing climate are complex, farm­ers have shown a considerable capacity to reduce emissions from agriculture and adapt to climate change by adopting appropriate agricultural practices and systems. To man­age current climatic risks and increase resilience to likely future changes, mitigation measures such as cultivation practices that increase soil carbon sequestration, manure management and reforestation need to be continued. The earlier and stronger the cuts in emissions, the quicker con­centrations will approach stabilization (although the effects

13 Greenhouse gases and clouds in the atmosphere absorb the majority of the long-wave radiation emitted by the Earth's surface, modifying the radiation balance and, hence, the cli­mate of the Earth. The primary greenhouse gases are of both, natural and anthropogenic origin, including water vapor, carbon dioxide (CO2), methane (CH4) nitrous oxide (N2O) and ozone (O3), while halocarbons and other chlorine- and bromine-containing substances are entirely anthropogenic.

of such measures on the climate will only emerge several decades after their implementation). Regardless of these mitigation measures, global warming will continue and the associated climate changes during the 21st century are ex­pected to exceed any experienced in the past thousands of years over which agriculture has been practiced in the NAE region. While mitigation measures clearly need to be pur­sued to reduce emissions from agriculture, some changes are now inevitable and will require adaptation responses.
     Large parts of North America and Europe are located in the temperate climatic zone characterized by favorable agroclimatic conditions, i.e., neither too dry nor too hot— with ample, well-distributed rainfall and relatively mild winters. The NAE region also includes areas in which cur­rent climatic risks such as drought, frost and flood play a considerable role, but the risk-prone areas are proportion­ately smaller than in other regions. Drought-prone regions include large parts of southwestern US, the Canadian Prai­ries and the Mediterranean, while frost risk and low temper­atures limit agricultural activities in large parts of Canada, the Nordic countries and Russia. The highest emissions of greenhouse gases from agriculture are generally associated with the most intensive farming systems whereas some of the low input farming systems currently located in marginal areas may be the ones that are the most severely affected by climate change (IPCC, 2007b).
     Agriculture contributes significantly to methane and nitrous oxide emissions. Land-use change can also provide a significant contribution to carbon dioxide emissions, but emissions connected to the use of fossil fuel for machinery and heating are considerably worse (Figure 5-4) (Rosenz-weig and Hillel, 2000; Stern et al., 2006; UNESCO, 2006a). In the NAE region, greenhouse gas (GHG) emissions from agriculture are in the range of 7-20% of total country emis­sion inventories (in terms of radiative forcing). Latest es­timates suggest that agriculture accounts for 48% of CH4