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Climate refers to the average weather experienced in a region over a long period, typically at least 30 years. This includes temperature, wind and rainfall patterns. The climate of the Earth is not static, and has changed many times in the past in response to a variety of natural causes.

Recent observed changes in global climate are likely to be due to a combination of both natural and human causes. The Earth's climate varies naturally as a result of interactions between the ocean and the atmosphere, changes in the Earth's orbit, fluctuations in energy received from the sun and volcanic eruptions. The main human influence on global climate is likely to be emissions of greenhouse gases such as carbon dioxide (CO2) and methane. At present, about 6.5 billion tonnes of CO2 is emitted globally each year, mostly through burning coal, oil and gas for energy.

The United Nations define the term climate change as refering only to changes in climate which can be attributed to human activity.

The Earth is kept warm by the greenhouse effect. Certain gases in the atmosphere (so-called greenhouse gases) absorb energy that is radiated from the Earth’s surface, and so warm the atmosphere. The greenhouse effect is a natural phenomenon without which life on Earth as we know it would not be possible, as the Earth would be 30°C cooler. However, our modern lifestyles have resulted in us releasing large amounts of greenhouse gases – like carbon dioxide and methane – into the atmosphere, enhancing the greenhouse effect and so pushing up temperatures globally. 

• See also IPCC AR4 FAQ 1.2 and 1.3. 

Average surface air temperature is the most useful way to describe the state of global climate. Data comes from millions of thermometer measurements taken around the world from as far back as 1860. Instrumental observations over the past 150 years from around the world show that temperatures have risen.

Image taken from IPCC AR4 WG1.

Expressed as a global average, temperatures have increased by nearly 0.8°C since the late 19th century and have risen by about 0.2°C per decade over the past 25 years.  The ten warmest years on record have all occurred since 1990, with 1998 as the warmest and it is likely that the last 100 years were the warmest century in the last millennium.

The increase in global temperature has been accompanied by:

• An increase in night-time temperatures over many land areas at about twice the rate of day-time temperatures.

• An increase in the length of the freeze-free season in many Northern Hemisphere mid-to-high latitude land areas.

• More intense rainfall events over many Northern Hemisphere mid-to-high latitude land areas.

• A near worldwide decrease in mountain glacier extent and ice mass.

• A decrease in Northern Hemisphere sea-ice amounts and a substantial thinning of Arctic sea-ice in late summer.

Climate change in the UK can be measured in records extending back over 350 years. One of the longest continuous temperature records in the world - the Central England Temperature (CET) series – shows that temperatures have increased by 0.7°C in the UK since 1659. Of that, a rise of around 0.5°C occurred in the 20th century. (Source: Hadley Centre).

The 1990s was the warmest decade in central England since records began, and 8 of the 10 warmest years since 1659 have occurred since 1990. The warming over land has been accompanied by warming of UK coastal waters.

Other climate indicators show a variety of changes for the UK climate:

• The growing season for plants in central England has lengthened by about one month since 1900. 

• Heatwaves have become more frequent in summer, while there are now fewer frosts and winter cold spells.

• Winters over the last 200 years have become much wetter relative to summers throughout the UK.

• A larger proportion of winter precipitation (rain and snow) now falls on heavy rainfall days than was the case 50 years ago.

• After adjusting for natural land movements, the average sea level around the UK is now about 10cm higher than it was in 1900.  

• See also the UKCIP briefing note on the warmest years in the UK and globally and IPCC AR4 FAQ 3.1, 3.2, 3.3 and 4.1.

Most climate scientists agree that the world is going to get warmer. The Intergovernmental Panel on Climate Change (IPCC) was set up by the World Meteorological Organization and the United Nations Environment Programme in 1988 to assess scientific and socio-economic information on climate change and its impacts and to advise the United Nations Framework Convention on Climate Change.

In 2007, the Fourth Assessment Report from the IPCC reports that the likely range of global average warming by the end of this century is between 1.1 and 6.4°C, relative to 1980-1999.

The range of projections reflects a number of uncertainties, including those associated with the climate models and feedbacks, natural climate variabity and future emissions of greenhouse gases.  

In 2007, the IPCC concluded that “most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations”. This is an advance since their previous (2001) conclusion that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations”. Discernible human influences now extend to other aspects of climate, including ocean warming, continental-average temperatures, temperature extremes and wind patterns.

Recent temperature rises can only be explained by human activities, as illustrated in the graphic below. Computer models that simulate climate demonstrate that other variations, such as the sun’s output and changes in volcanoes (shown below as blue ‘plumes’) cannot account for all the observed warming (black line). Only when both human activities and natural variations are included in the models do they match the observed changes (pink plumes).
 

From IPCC AR4 WG1.

Recent work by scientists at the Met Office has also examined the 2003 summer heatwave. Based on analysis of the observational record of summer temperatures in Europe, they estimate that it is very likely (>90%) that human influence at least doubled the risk of a heatwave of this magnitude occurring (Stott PA, Stone DA and Allen MR, 2004 in Nature 432, 610-614, 02 Dec 2004). 

• See also IPCC AR4 FAQ 2.1, 6.2 and 9.2. 

Experiments using global climate models show that when we reduce emissions of carbon dioxide, we reduce the rate of rise of average global temperatures and so lessen the rate and impacts of climate change. We can therefore slow the rate of warming by changing our behaviour.

However, once released into the atmosphere, carbon dioxide remains there for about 100 years. So even if we were to reduce emissions, we are committed to a certain amount of warming. In 2007, the IPCC concluded that if all greenhouse gas emissions were held at 2000 levels, a further global average warming of 0.3 to 0.9°C can be expected by the end of the century owing to greenhouse gases currently in the atmosphere. 

• See also IPCC AR4 FAQ 10.3. 

Global warming refers to the increase in the average temperature of the Earth’s atmosphere. Climate change refers to the changes in climate that might accompany the warming of the atmosphere, such as changes in the frequency and intensity of extreme weather and sea level rise. Many people use these expressions interchangeably. However, the word warming may be misleading, as it doesn’t embrace the full range of changes that could result.

• See also IPCC AR4 FAQ 11.1 

The climate of the UK is affected by the Gulf Stream, which brings warm water from the Gulf of Mexico across the Atlantic Ocean to north west Europe. This warm water keeps the climate of the UK warmer than continental locations at similar latitudes. Some scenarios of climate change suggest that with further climate change, the North Atlantic Thermohaline Circulation (THC), of which the Gulf Stream is a part, could shut down. If this were to happen, average temperatures in the UK would drop by some 4°C. Research at the Met Office shows that global warming could reduce the strength of the THC circulation by 25% by 2100. However, the direct heating from global warming would be greater than any cooling effect from reduced activity of the THC. A cold future is therefore very unlikely.

• See also the UKCIP briefing note on potential slowing of THC and IPCC AR4 FAQ 10.2. 

Greenhouse gases are naturally occurring gases in the atmosphere that have the capacity to absorb long-wave radiation emanating from the Earth’s surface. By absorbing this energy and re-radiating it, the gases cause the temperature of the Earth’s lower atmosphere and surface to increase. The most common greenhouse gases are water vapour and carbon dioxide. Others include methane and nitrous oxide. Man's activities have increased concentrations of all of these gases and have also introduced new ones, such as CFCs. 

• See also IPCC AR4 FAQ 7.1. 

Oceans absorb heat from the atmosphere. As the atmosphere warms, so too do the oceans. When water is warmed, it expands, causing sea levels to rise. In addition, as the temperature of the oceans and atmosphere increases, so permafrost, glaciers and ice sheets melt, releasing additional water into the oceans and contributing to sea level rise.

In addition, the UK and northern Europe are still responding to the melting of ice sheets that covered the land during the last Ice Age. In response to this, mainland Britain is slowly tilting, with South and East England slowly sinking into the sea and the North West and Scotland rising. Sea level rises around the UK would increase the risk of flooding and coastal erosion. 

• See also the UKCIP briefing note on sea-level change estimates for the UK and IPCC AR4 FAQ 5.1. 

The type, frequency and intensity of extreme events such as heatwaves, droughts and floods are expected to change as the Earth’s climate changes.

In a warmer future climate, there will be an increased risk of more intense, more frequent and longer-lasting heatwaves, such as the European heatwave of 2003. Most global climate models project that a warming of future climate results in increased summer dryness and winter wetness for many places in northern middle and high latitudes (like the UK), indicating a higher risk of winter flooding and summer droughts.

With more energy in the climate system, it is also possible that storms and hurricanes could become more severe in future, but the climate models do not give consistent findings.

Conversely, it is also important to remember that individual extreme events cannot be taken as proof that the climate is changing. 

• See also the UKCIP briefing note on climate change and hurricane activity and IPCC AR4 FAQ 9.1 and 10.1. 

The UK Climate Impacts Programme works closely with the Hadley Centre for Climate Prediction and Research at the Met Office and the Climatic Research Unit and Tyndall Centre for Climate Change Research both at the University of East Anglia. The Hadley Centre have produced a useful briefing note on the science behind climate change and the greenhouse effect.

The definitive source of information about climate science is the Intergovernmental Panel on Climate Change (IPCC). The IPCC was established in 1988 by the World Meteorological Organisation (WMO) and the United Nations Environmental Program (UNEP). Its role is to assess on a comprehensive, objective, open and transparent basis the scientific, technical and socio-economic information relevant to understanding the scientific basis of risk of human-induced climate change, its potential impacts and options for adaptation and mitigation. The fourth and latest IPCC Assessment Report, AR4, was published in 2007.

The BBC has an extremely comprehensive section on climate change, including a simple Q&A page and an animated guide.

The earlier you find out the likely impacts, the more options you have for adapting, including taking advantage of opportunities. This is particularly important when it comes to major investment decisions and decisions that may affect whole sectors, or communities. In addition, the sooner we take action to reduce emissions, the greater the chance of stabilising the climate.

The UK will be warmer and this will certainly bring some potential opportunities. However, we are also likely to experience more extreme weather and we need to start planning now to deal with the consequences, such as additional flooding, drought and sea level rise. There are also likely to be serious implications for other parts of the world, and effects on, for example on the global trade network, that will have an impact on the UK.

There is a lot of work going on to reduce greenhouse gas emissions and so to limit the impact of climate change. Some climate change is inevitable because of the emissions human activity has already released, so UKCIP was set up by the UK Government to co-ordinate research into the impacts of climate change and to help organisations assess how they will be affected so they can plan to adapt. This in itself is a major task. UKCIP’s work on climate change adaptation is complementary to the work going on to limit climate change.

Other organisations have been set up by the UK Government to provide help and advice on the reduction of greenhouse gases. Foremost of these are the Carbon Trust and the Energy Saving Trust.

UKCIP does not fund research itself. To date, most research into the impacts of climate change has been undertaken in partnership, with each organisation contributing according to their budget. Feel free to contact us for advice if you are interested in undertaking research into climate change impacts and adaptation.

The climate scenarios provided by UKCIP do not provide any information on changes expected in the short term (i.e. next few years). Short term projections of climate (and climate change) are difficult due to the dominance of natural climatic variability (such as that produced by El Nino Southern Oscillation) on annual or decadal time-scales.

In 2007, scientists at the Met Office Hadley Centre produced their first decadal climate projection. It suggests that over the period from 2004 to 2014, average global temperature might rise by 0.3°C. In the years up to 2009, natural climatic variability is anticipated to partially offset the anthropogenic global warming signal. However climate is expected to continue to warm, and half of the years between 2009 and 2014 are expected to exceed the warmest year currently on record.

The climate scenarios provided by UKCIP do not say anything about how the projected changes might affect the frequency of or areas at risk from flooding.

The Environment Agency (EA) of England and Wales and the Scottish Environmental Protection Agency (SEPA) can advise you as to whether your property is in the floodplain and offer information on how to protect yourself, your family and your property against flooding.

The EA flood pages can be found here. The SEPA flood pages can be found here. Both pages include interactive flood maps that allow you to search for areas of flood risk based on postcode.

International negotiations, including the Kyoto Protocol, were established and are overseen by the United Nations. For more information visit the UN Framework Convention on Climate Change (UNFCCC) website.

As with the current generation of numerical weather forecasting models, climate models can be run as an ensemble with the same external forcing but slightly different initial starting conditions. The resulting differences of individual ensemble members from year-to-year are therefore an indication of the natural variability in the ocean-atmosphere system. For climate change analysis, this background natural variation is typically referred to as noise, with the change due to increasing greenhouse gas emissions is the main signal of interest. The noise is reduced by averaging out the individual variations using the ensemble mean.

The Hadley Centre Regional Climate Model (HadRM3) is very computer intensive. For this reason, only three simulations have been run to assess natural variability, and this has only been undertaken for the A2 (Medium-High) emissions scenario. The A2 ensemble data can be obtained from the British Atmospheric Data Centre (BADC) and a comparison of the range of individual ensemble members at a particular time will allow an analysis of natural variability. For some variables, such as precipitation, this natural variability is very important, both year-to-year and decade-to-decade.

The UKCIP Scenarios Gateway also offers monthly mean temperature time-series output with 5 km spatial resolution. Each monthly value represents the average of the three simulations. These data are freely available to licensed users through the UKCIP02 data pages. A tool (ProMPTS) has been developed to help interrogate and interpret the monthly time-series, and is available on the UKCIP02 extras page. The range of the simulated change through time gives an indication of natural climate variability.

Yes. The Gulf Stream (properly termed the Thermohaline Circulation or North Atlantic Drift) carries warm upper waters northwards and returns cold water towards the equator. This ocean current is partially responsible for the UK 's relatively mild climate and is driven by the sinking of dense saline cold water off Labrador and Greenland. The Hadley Centre climate model, which includes ocean circulation, predicts that North Atlantic thermohaline circulation strength will fall under all four emissions scenarios by around 15-25% by 2100. This leads to a corresponding decrease in the amount of heat transported towards the UK, but this is more than offset by the direct greenhouse warming. As they are taken from the same experiment, this effect is taken into account in the UKCIP02 climate change scenarios. None of the standard Hadley Centre model simulations (and indeed none of the global climate models used in the IPCC Third Assessment Report) show a complete shut-down by 2100. For more information see Chapter 7 of the UKCIP02 Scientific Report and the subsequent UKCIP guidance note Slowing of the Atlantic meridional overturning circulation at 25 degrees North. Research into the Thermohaline circulation is ongoing by many research centres including the Hadley Centre and NERC (through the RAPID research programme).

Climate models are a mathematical description of our understanding of the processes in the Earth's climate system; atmosphere, ocean, land, cryosphere. We evaluate their reliability in a number of ways. Firstly by comparing their representation of the current climate and observations, including not just means but variability and extremes. Secondly, by driving them with the best estimates of changes to climate forcings over the last 150 years (natural, such as volcanoes and solar radiation, and man-made such as greenhouse gases and aerosols) and comparing the simulation of climate change from the model (sometimes called a ‘hindcast') with observations of trends (in, for example, global mean temperature) over the same period. Lastly, some validation can be carried out by comparing model simulation of climates many thousands of years ago with reconstructions of climate of the period (so called palaeoclimatologies). Validation exercises such as these provide compelling evidence that, at least in terms of gross temperature response, the model is effectively reproducing what has been observed, and this gives us confidence that the models are adequate tools for the prediction of future climates, albeit with the uncertainty described in Section 3.5 of the UKCIP02 Scientific Report. More detail on model validation and performance can be found in Chapter 8 (Model Evaluation) of IPCC Third Assessment Report. (Source: Climate Change and the Greenhouse Effect, Hadley Centre, December 2005).

Although they are made by the same sort of mathematical model, weather forecasts and climate scenarios are 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; it might say, for example, that there will be a band of heavy rain moving across Somerset tomorrow mid-morning.

A climate change scenario tells us about changes in the average climate, its variability and extremes. For example, it might say that the average temperature of summers in Somerset in 40–60 years time will be 4 degrees higher than currently, it will receive on average 25% more rain in winter with three times the current number of heavy rainfall events, and 50% less rain in summer. It will not make a specific forecast such as it will be raining in Somerset on the morning of 15 October 2044. (Source: Climate Change and the Greenhouse Effect, Hadley Centre, December 2005).