Food & Climate 

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From industrial development to global changes

Increase in carbon dioxide

Through burning fossil fuels and eradication of forests, human activity has caused the carbon dioxide (CO₂) concentration of the atmosphere to increase by some 25% since the industrial revolution, and that increase continues.

CO₂ plays an important role in inhibiting the escape of the heat radiated by the earth. The sun beams short-wave radiation to the earth, which sends long-wave radiation back to space. Greenhouse gases in the earth’s atmosphere (carbon dioxide, water vapour, methane, nitrous oxide, and the chlorofluorocarbons) absorb the outgoing radiation, thereby holding heat near our planet. This process occurs naturally: without the natural greenhouse effect, our planet would be near freezing. Instead, this process warms the earth to its current mean temperature of about 15ºC.

1. Measurements made on Mauna Loa in Hawaii since 1956 reveal the recent CO2 trend
Source IPCC

The greenhouse effect

The concern now is that human activities are causing the natural greenhouse effect to be augmented, leading to significant changes in the temperature and related changes in the entire climate system. Has global warming actual begun? When we look at the Earth’s global average temperature over the last century, we find that temperatures have risen about 0.5ºC. The decade of the 1990s is the warmest on record. While it is difficult to prove conclusively that rising CO₂ is causing the earth to warm, scientists believe that the two trends -- increasing carbon dioxide and increasing temperatures – are likely to be linked (IPCC, 1996a).

Climate Change Scenarios

Because the earth’s climate system is too large to allow controlled experiments, scientists have been employing mathematical models, known as global circulation models (GCMs), to assess the processes known to occur and their possible interactions. Such models are used to forecast the trend of climate over the coming decades. Their results are still tentative and should not be accepted uncritically. However, we should examine the implications of their predictions, while continuing to look for the emerging empirical evidence of changing climate.

At least ten GCMs have been developed by atmospheric scientists in various research groups and have been used to project the effects of greenhouse gas increases. Results from these simulations show a mean global warming in the range of 1.4 to 5.8ºC by the end of the next century. When the effects of sulphate aerosols are included in the projections, the best estimate for 2100 is a temperature increase in the range of 1.0 to 3.5ºC. The latter projections are somewhat cooler since sulphate aerosols from industrial pollution tend to cool the earth’s atmosphere by reflecting short wave solar radiation. Global climate models also predict an increase in mean global precipitation ranging from about 5 to 20% due to the fact that a warmer atmosphere can hold more water vapour.

GCMs further predict that:

• The high latitudes and high elevations are likely to continue to experience greater warming than the global mean warming, especially in winter.

• Winter and night time temperatures (minimum temperatures or TMINs) are projected to continue to rise disproportionately.

• The hydrological cycle is likely to further intensify, bringing more floods and more droughts.

• More winter precipitation is projected to fall as rain, rather than snow, decreasing snow pack and spring runoff, potentially exacerbating springs and summer droughts.

3. Changes in temperature and precipitation
Source: NASA/GISS

The Figure shows future changes in temperature (left) and precipitation (right) simulated with the Hadley Model for the year 2050. The changes are more severe in the later part of the century.

Sea level rise scenarios

Global warming will also affect the sea-level. There has been a range of estimates for sea-level rise based on greenhouse gas emissions, and temperature projections that affect the expansion of the water in the oceans, and glacial melting. Because some coastal areas are sinking and others rising, sea-level rise scenarios are added to current trends. Recent estimates are on the order of a 0.5 m rise by 2100.
If you would like to know more about Sea Level Rise causes and consequences go to Oceanography

Socio-economic Scenarios

Climate is not the only factor that will be changing as the twenty-first century unfolds. Population growth and changing economic and technological conditions are likely to affect world society and the environment even more than changes in climate. It is important to take such changes into account in climate change impact analyses: first, because climate change will occur not in the present but in the future, and second, because such changes may affect the sensitivity of agriculture (or other sectors) to climate change. However, predicting population growth rates and future economic conditions is equally if not more uncertain than predicting the future climate.

 A useful approach is to contrast "optimistic" and "pessimistic" views of the future. In the optimistic scenario, population growth rates are low, economic growth rates and incomes rise, environmental pollution decreases and land degradation abates. In the pessimistic scenario, population growth rates are high, economic growth rates and incomes are low, environmental pollution increases, and land degradation accelerates. A scenario of no change (i.e., present conditions) should also be included. The differential effects of climate change on current conditions, and on these two alternative scenarios of the future may then be evaluated.

Related pages:

For more information about sea level rise: 
Oceans - More - Oceans and climate - Sea level rise

To know more about the consequences of climate change for humans go to:
People changing climate - More - How will future be?

Author:  Marta Moneo and Ana Iglesias- Universidad Politécnica de Madrid - España
1. Scientific reviewer: Alex de Sherbinin - CIESIN, Columbia University - USA
2. Scientific reviewer: Lily Parshall - Goddard Institute for space studies, Columbia University - USA
Educational reviewer: Emilio Sternfeld - Colegio Virgen de Mirasierra - España
Last update: 12/05/2004