The Science of Global Warming; Evidence of Climate Change Is Based on Years of Research and Thousands of Critically Reviewed Scientific Studies, as Professor Ian Hall of Cardiff University Explains
Byline: Ian Hall
THE key to understanding global climate change is to first understand what the Earth's climate system is, how it operates and the changes it is capable of.
The Earth's climate system is a complex interaction between the atmosphere, the oceans and ice sheets (the cryosphere), living things (the biosphere), and soils, sediments and rocks.
These components all affect how the heat energy from the sun is redistributed around the globe from warmer to colder places.
This global movement of heat drives our weather systems, and we experience the effects as the 'average weather' across Wales.
This input is balanced by an output as the Earth's surface warms and radiates heat energy back into space.
If the Earth was in perfect energy balance, the temperature averaged across the planet's surface would be -19[bar]C - much colder than the typical surface temperature we currently enjoy (around 14C).
The reason the Earth's surface is warm enough to sustain life is the presence of greenhouse gases within the atmosphere.
These gases, which include water vapour, CO2 and methane, have a direct effect on the amount of heat energy that is trapped within the lower atmosphere, rather than escaping into space. If the concentration of CO2 in the atmosphere doubles, the 'resulting global average warming will very likely be between 2-4C - a good bet would be 3C, with the remaining uncertainty due to additional climate interactions, known as feedback effects.
Climatologists worldwide are working on reducing these smaller uncertainties, and predicting the regional effects of climate change, while the overall picture of global warming as a result of increased CO2 is inescapable.
The concentration of atmospheric CO2 has risen sharply over the past 150 years, from a pre-industrial value of 280 parts per million (ppm) to 385ppm today.
In 1850, levels of atmospheric CO2 were similar to those of the warmest intervals of the past 700,000 years.
Current levels of atmospheric CO2 are higher than they have been for several million years, and are similar to those in a very ancient time, when Earth's climate was warmer, and sea levels were significantly higher than today.
The current rise in CO2 is caused entirely by human activity and is primarily the result of burning fossil fuels, with a smaller contribution due to deforestation.
We know this because many independent observations show that the carbon content has also increased in both the oceans (leading to ocean acidification) and the land biosphere (after subtracting deforestation).
The ocean and land biospheres are the only stores of carbon that could provide a natural source of CO2 to the atmosphere on century timescales. Had they done so, they would currently hold less carbon, not more as is observed.
Observations of the climate system are crucial to establish actual climate trends.
In addition, climate models are used to predict how values such as global average temperature or sea level may be expected to respond in the future.
Since the beginning of the 20th century, global average climate has warmed by about 0.8C. Temperatures during the last decade have been the highest since measurements began in the mid-19th century and for many centuries before that. …