The Greenhouse Effect
The Earth's temperature is determined by the amount of sunlight received which warms the surface of the plannet and the amount of infra-red emissions given off by the Earth's surface as it cools down. Some of this infra-red radiation is trapped by the presence of gases in the atmosphere that prevent heat escaping. this process is known as the 'greenhouse effect' and the gases that keep the heat in are called greenhouse gases.
Carbon dioxide is the main greenhouse gas by volume. human use of fossil fuels increases the amount of carbon dioxide emissions given off and trapped in the atmosphere. This increases the Earth's temperature. methane is another more powerful greenhouse gas. Concentrations of atmospheric methane are also affected by human activity either through increased levels of emission or by triggering chemical processes that reduce the natural rate of decay of atmospheric methane.
The Government's Energy White Paper (2003) details some of the effects of temperature rise around the planet:
- retreating ice caps on many mounbtain peaks
- global mean sea level rise of 1-2 mm each year during last century
- summer and autumn Artic Sea ice thinned by 40% in recent decades
- more frequent, more intense El Nino events during last 20-30 years
- decrease in global snow cover by 10% since 1960's
- weather related economic losses increased 10 fold in last 40 years.
Local Impacts
A recent NWRA commissioned paper assessed the likely impacts of climate change on the North West based on 2002 scenarios from the Climate Impacts Programme. this report suggests annual average daily temperatures in Cumbria will rise between 1 and 2 degrees by 2050's and by between 1 and 4 degrees by 2080's depending on the level of greenhouse gas emissions. Summer rainfall is expected to reduce by as much as 15% in Cumbria by 2020's irrespective of low or high levels of emissions. By 2080's summer rainfall will decrease by between 30% and 45% depending on whether there is a low or high emnissions scenario. modelling winter rainfall in Cumbria shows a consistent increaseof up to 15% throughout the first half of the century rising to somewhere between 15% and 30% increase by 2080's depending on emission levels.
Snowfall in Cumbria is forecast to decrease dramatically, initially a 10% decrease by 2020's reducing to between 35% and 55% of current levels by 2050's and to between 45% and 85% of current levels by 2080's depending on high or low emission levels. in many parts of Cumbri snow may disappear altogether as we enter the last quarter of the century.
Predicted changes in sea level do not appear to be available for Cumbria but UK sea levels are generally predicted to rise by between 7 and 36 cm by 2080. Increased frequency of flooding around rivers and the coastlie is one likely consequence. Forecasting the effects on biodiversity in Cumbria is not clear-cut. milder winters suggest the earlier appearance of leaves on trees, of migrating species like swallows and insects, including agricultural pests and earlier breeding times for many species.