Across the globe, in response to increases in heat-trapping gases such as carbon dioxide (CO2) in the atmosphere, temperature and precipitation patterns are changing.
The rate of climatic change in the next century is expected to be significantly higher than it has been in the past. At our current rate of emissions, the Intergovernmental Panel on Climate Change (IPCC) estimates that CO2 levels in the atmosphere will double or triple during the next century, and the climate system will respond.
It is expected that due to change in climate some changes will be slow and some rapid. The rapid changes could be the retreating or vanishing glacial ice, disappearance of year-round sea ice in the Arctic and replacement of polar tundra by conifer forests.
The slow changes could be the changes in melt patterns on Greenland Ice Sheet, increased rates of flows of ice streams in Greenland and Antarctica , increase in thermal expansion of ocean, disappearance of West Antarctic Ice Sheet, ocean acidification and decreases in ocean oxygen levels.
Despite of fact that earth will always have distinct seasons because of its tilted axis, one expected signal of climate change is a shift in the length and character of summer and winter seasons. In general, summer temperatures will arrive earlier than they currently do, especially at high latitudes.
Additionally, they will be hotter and last longer than they do now. Future winters will arrive later and be shorter and warmer. Around the world, climatologists have already observed increases in the number of days of record heat, and concurrent decreases in the number of days of record cold.
In the future it is thought that the increase in CO2 and other greenhouse gases will cause an increase in global mean temperature, with larger increases at high latitudes than elsewhere and larger increases during winter than summer.
Climate change will affect agriculture through effects on crops and weeds, soils, insects and disease. In terms of crops, the main climatic variables that are important are temperature, solar radiation, water and atmospheric CO2 concentration,
Whilst plant development is generally increased by temperature, CO2 enrichment can accelerate it even further in some cases, whilst in other cases it may have no effect or retarding effects in other cases.
Concentrations of CO2 in the atmosphere have increased from pre-industrial levels of about 270 μmol mol−1 to current concentrations of 360 μmol mol−1.
Increases in greenhouse gases in the atmosphere, such as CO2, methane and nitrous oxide, are predicted to result in a rise in mean temperatures of 2–3°C by the year 2050 and even by as much as 4.5°C by 2100 AD together with more frequent episodes of water deficit and higher temperature events.
Plant growth and crop yields depend on temperature and temperature extremes. The optimum range for C3 crops is 15–20°C and for C4 crops it is 25–30°C. The variation in temperature requirements and temperature extremes of different cultivars of the same species, and among species, is quite wide for most crops.
C3 plants are sensitive to higher CO2 and typically respond with an increase in photosynthesis and growth, whilst C4 plants don’t respond so dramatically.
Typically, field-grown crops, such as winter wheat, carrot, cauliflower and onion, have been shown to increase leaf area and biomass during early crop growth under elevated CO2 conditions compared with ambient conditions.
Whether current plants and animals will be able to adapt to upcoming changes in climate remains an open question. Just as in past climatic shifts, some species will flourish while others will struggle, or simply vanish. Exactly how future climate will develop is an ongoing question – one that is being closely monitored by scientists and citizens around the world.
CO2 enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are usually markedly altered; this includes increased leaf expansion and cell wall extensibility and often cell turgor pressure, leading to increased leaf and root growth.
If increased turgor pressure is alone insufficient to account for increases in leaf growth under elevated CO2, then cell wall relaxation (extensibility), cell division or both may also be affected.
Simplistically, scientists have suggested that increased leaf size, if associated with larger cells, suggests that cell expansion has been stimulated, whilst increased leaf size, if associated with more cells, suggests that cell division has been stimulated.
Contrasting seasonal growth responses to elevated CO2 and temperature in certain species suggests that pasture management may change in the future. The grazing season may be prolonged, but whole-season productivity may become more variable than today.
This is shown by studies of perennial ryegrass where, in spring, increased leaf extension occurred in elevated CO2 whilst in summer it was reduced. In high temperature it was reduced in both seasons.
In elevated CO2 and temperature, leaf extension increased in spring, whilst in summer it decreased. Many organisms are near their tolerance limits and some may not be able to persist under hotter conditions.
Higher temperatures in arid regions with cold winters may mean spring growth occurs earlier. Water reserves gained during the winter may, in some cases, be depleted earlier.