The Earth is warming faster than it has in the past thousand years, hence the term global warming. But climate change is a better description than global warming, as some areas may, in fact, cool. It also describes other effects like rising sea levels and more extreme weather.
Carbon dioxide (CO2) is a greenhouse gas, as are methane, water vapour, nitrous oxide and ozone. The fundamental physics that links CO2 concentrations to temperature changes has been known since the late 19th century.
No: The 'greenhouse effect' is the way the atmosphere traps some of the energy we receive from the Sun (infrared radiation or heat, ultraviolet and visible light) and stops it being transmitted back out into space. Earth receives energy from the Sun and re-emits it back to space. The atmosphere traps some of the outgoing energy and warms Earth. This is known as the greenhouse effect. Without this natural greenhouse effect, Earth would be some 30 °C colder, and life as we know it would not be possible.
The problem is that scientists believe we are adding dangerously to the natural greenhouse effect with the gases from industry and agriculture. This traps more solar energy and increases the temperature.
There is little doubt, from the evidence so far, that there have been enormous changes in climate in the past. These ranged from a complete absence of ice over the Poles to ice sheets extending across much of Europe, Asia and North America. The last major extension of polar ice retreated only 10,000 years ago.
Natural sources, such as tree rings and glaciers, as well as human records, show that climate has changed significantly over the past few hundred years. There was a relatively warm period in Europe during the 14th century, followed by a quite sudden change to cooler conditions in the 15th century. This extended into the Little Ice Age of the 17th and 18th centuries, followed by a warming trend that has recently accelerated. The evidence for this recent warming comes largely from direct measurements of temperature. In the more temperate northern latitudes, winters are less severe than 30 years ago, with cold snaps generally being short-lived.
The ten warmest years on record have occurred since 1998 (as of July 2011). 2010 saw a relatively strong La Niña, but globally was still one of the warmest years on record.
Records of past variations in CO2 concentrations from ice core records The scientific consensus states that it is very likely that most of the warming over the last 50 years is a result of greenhouse gas emissions caused by human activity.
The exchange of 'man-made' carbon dioxide between man-made emissions, atmosphere, ocean and land, is about 7 GtC/year (billion tons of carbon, in the form of carbon dioxide, per year), which also shows much larger natural exchanges between atmosphere and ocean (about 90 GtC/yr) and atmosphere and land (about 60 GtC/yr). However, these natural exchanges have been in balance for many thousands of years, leading to the pre-industrial concentration of CO2 remaining steady at about 280 ppm.
CO2 concentrations in the atmosphere are rising. They have increased by about 38% since industrialisation began, from 280 ppm (parts per million) to 387 ppm. Two-thirds of that increase has occurred in the last 50 years. CO2 levels are now 30% higher than at any time over at least the last 800,000 years.
Past, current and future changes in temperature relative to 2000 This is the fundamental difference between weather and climate. Even in a warming climate we will still get individual weather systems which will bring 'miserable' weather. Increasing greenhouse gas concentrations will mean an upward trend in temperatures. However, natural variability in the climate means that not every year will necessarily be warmer than the last, with some years being cooler and others warmer.
There is indisputable evidence that the climate is changing. The average global surface temperature has risen by 0.6 °C in the past 140 years. Globally, nine out of the ten hottest years ever recorded have occurred since 1990. Here in the UK, four out of five of the hottest years ever recorded over a 330-year period have occurred since then.
A research project, carried out by Met Office and the Centre for Ecology and Hydrology, looked at extreme flooding in October and November 2000. It concluded that, though the events were extreme, they could not in themselves be attributed to climate change. However, heavy rainfall and peak river flows of similar duration have been increasing in frequency and magnitude over the past 50 years. This pattern is consistent with model predictions of how human-induced climate change affects rainfall.
Experts predict that fierce storms and floods, such as those that brought chaos to parts of the UK in October 2000, are likely to become more frequent in the future. Over the past 100 years, warming has been accompanied by a reduction in the frequency of frosts and an increase in the number of heatwaves in many parts of the world. The amount of rainfall is getting heavier in some countries in terms of volume per downpour.
Although they are made by the same sort of mathematical model, weather forecasts and climate predictions are really quite different. A weather forecast tells us what the weather (for example, temperature or rainfall) is going to be at a certain place and time over the next few days.
A climate prediction tells us about changes in the average climate, its variability and extremes. So, it might say that Somerset, in 40-60 years time, will have, on average 25% more rain in winter with three times the current number of heavy rainfall events. It does not forecast that it will be raining in Somerset on the morning of 15 October 2044.
The two major ice sheets are on Greenland and in the Antarctic. The Greenland Ice Sheet contains enough water to contribute about 7 m to sea level, and the West Antarctic ice sheet (WAIS), which is the part of the Antarctic ice sheet most vulnerable to climate change, contains about 6 m.
A sustained rise in local temperatures of about 3 °C, equivalent to a global-mean warming of about 1.5 °C, which is likely to be reached by the end of the century if man-made emissions are not controlled, would melt the Greenland Ice Sheet, although it is estimated that this would take a few thousand years. A major collapse of the WAIS is thought to be very unlikely during the 21st century, although recent measurements suggest that contributions to sea-level rise from this source may be greater than previously estimated.
The impact of climate change - specifically global warming caused by the burning of fossil fuels - on tropical cyclone activity is the subject of ongoing debate and research in the scientific community. Although there is no clear consensus on whether global warming is currently having any measurable impact on tropical cyclones, climate models indicate that there may be an increase in tropical cyclone intensity in the future, while tropical cyclone frequency will either remain unchanged or decrease.
Learn more about tropical cyclones
There will be winners as well as losers. Warmer weather would allow a longer growing season in temperate latitude and reduce the need for heating. However, reduced rainfall in tropical regions can lead to the expansion of deserts and rises in sea level would threaten low-lying coasts and islands.
On present evidence, global warming could be slowed if emissions of methane and carbon dioxide were reduced. The main artificial sources of these gases are (a) for methane - agriculture, emissions from landfill sites and natural gas and (b) for carbon dioxide - the burning of fossil fuels, cutting down and burning trees. This may seem to be something that only governments or large organisations can tackle, but the individual can also contribute significantly by, for example, not using a car unnecessarily and recycling.
Last updated: 30 September 2013