The fact that the climate is changing is not in dispute. It has always, and always will change. We know it will change from the many elements at play, including those created by man. Where we are having difficulty is in understanding the relative impact of man and nature. Before man even existed nature was already at work.
It was creating some warmth, but it was also creating periods of devastating cold. That has not changed, and why would it? What's new is the current measurement and modeling of interactions and examination of their relative effects. This brings us to some key questions: has nature been usurped by mankind as the driving agent of change, and why has this happened?

Climate science is vital if we want to answer that question. There are many groups with an interest in its answer, outside the immediate caucus of scientists. These include the scientific and non-scientific media, energy providers, fossil fuel exploration companies, green activists, climate bloggers, investors, charitable organisations, politicians, governments, economists, bankers and the general public. A groundswell of beliefs, based on a multitude of scientific papers, which have been interpreted and commented upon, by both scientists and others, has generated much debate, leading to demands for action to reduce mankind's influence on the planet's climate. Burning fossil fuels to travel, keep warm, raise animals, create buildings, manufacture goods and keep healthy could be affecting the climate, particularly by raising global temperatures. Consequently, we are investing in wind and solar farms, debating the merits of harnessing wave energy, building more nuclear power stations, and developing alternative sustainable and carbon-free fuels. People are also now paying a premium for their energy to enable carbon trading. And more change may be on the way as society ramps up investment in alternative energy sources and climate change mitigating technologies. Consequently, the science of climate change has a great responsibility. It is beginning to have a profound affect on economic policy, including the allocation of resources for growing crops for fuel instead of for food, with all the implications that has for an increasing world population.

What is Science?

Science uses measurement and experiment to verify facts and increase our knowledge of the universe, and everything in it. In its basic form scientists collect data and then analyse the information to confirm or disprove hypotheses. For a hypothesis to be accepted requires it to be proven with at least a 95% confidence level. It may then be adopted as a theory or a mathematical model.

Scientists are also expected to publish their findings, and make data publicly available so that other scientists may repeat their experiments, or replicate their models, to check their conclusions. The result of this peer-review process should ensure only high quality findings are used as the basis for future research and the development of useful predictions. In the case of climate change science, which is a branch of natural science, the conclusions have a far-reaching impact on economic progress, health, and well being, as governments use the results of climate change science to formulate energy, and related, policy.

Natural science; the study of natural phenomena, is an empirical science, meaning it must be based on observable phenomena and capable of being tested for its validity by other researchers working under the same conditions. This is very important. It removes from the science any spurious findings, beliefs and prejudices and keeps science from becoming a religion, based on faith, or a doctrine, based on ignorance. At a lower level it removes bias, and ensures any hypothesis, resulting from the data, is free of individual preferences.

More about science as a religion may be found in Science as Religion.

More about peer-reviewed climate science may be found in the latest (AR4) United Nations Intergovernmental Panel on Climate Change (IPCC) report, published in 2007, which includes the names of many of the climate scientists working in the field in the IPCC Assessment Report. Note that the IPCC does not carry out any scientific research itself but 'interprets' peer-reviewed literature and submits its views to the UN and governments. This means that sometimes it ignores minority views or views with which it does not agree.

Underpinning most science is mathematics. It is used to define models of how things work, such as climate change. Data is often analysed using statistical methods, which is a branch of mathematics. This allows scientists to assess the reliability and variation in experimental results. Statistical analysis occupies a critical role in many areas of natural science. Computational science is also important in analysing and modelling data to simulate real world situations. In the case of climate science computer modelling has taken centre stage, some say at the expense of more basic data collection and analysis.

Scientists do their work mainly in academic establishments and are members of institutions, like The Royal Society (the UK's national academy of science), which publishes their findings in the scientific literature. It has written a strong rebuttal to climate change 'sceptics' in A guide to facts and fictions about climate change. Much of the money to fund scientific research comes from governments (as representatives of taxpayers), as well as commercial organisations (as representatives of shareholders and pension funds) that hope to profit from new knowledge. Scientists therefore sometimes feel pressured to work in areas that are being funded rather than in nascent and politically unfashionable areas.

Sometimes, research may be characterised as 'bad science'. This is research that is well intentioned, or sometimes politically motivated by governments or commercial organisations (which hope to profit from it), but is seen as incorrect, obsolete, incomplete, or promotes over-simplified explanations of natural phenomena.

Finally, science, as a body of knowledge, should never be regarded as complete, and the consensus or majority view should carry no more weight than a dissenting minority, if those views are based on scientific endeavour. No scientific progress is made without dissent. Science is a process of building a body of knowledge, and increasing understanding, and not just the knowledge itself.

Climate Change and Climate Science

Climate change is a phrase used to describe the process of long-term statistical variation in the weather. In current usage it also means recent weather events. 186 countries have signed the Kyoto Protocol since 1997 (not including the US). The Protocol is based on recommendations from the IPCC, set up by the UN in 1988, to provide a scientific basis for policy decisions. The IPCC interprets and summarises, mainly peer-reviewed scientific papers, on climate change, greenhouse gases and the effect of CO2 emissions. Many in scientific and non-scientific circles have accepted its findings, namely that the climate is warming, primarily because of increased greenhouse gases, particularly CO2, in the atmosphere. Whereas there is a balance in nature between sources and sinks of atmospheric CO2, the emission of additional CO2 by burning fossil fuel, and other activities, affects that balance. Climate models are predicting temperature increases from these man-made climate forcings, and these have been seen to happen. However, some scientists also believe these are part of the natural variation to be expected, particularly as the planet is still emerging from a mini ice age.

Climate changes include variations in mean temperatures¹ (in regions or globally) and the probability of extreme weather conditions. Climate forcings include variations in solar radiation, ocean currents, cloud cover, changes in the solar system's centre of mass, and variations in the composition of the earth's atmosphere. (Sunspots, are one of the main fluctuations in solar radiation, but there is also the solar wind and its effect on non solar cosmic radiation reaching the earth, which has an effect on cloud formation, and consequently on the amount of heat energy reaching the planet.

There are several climate change feedbacks that can either amplify or cancel climate forcings, and which are cyclical. Some elements (maybe not including El Nino) of the climate system, such as the oceans, which account for 70% of the planet's surface, absorb most of the energy from the sun. The oceans redistribute heat from the equator to the poles via currents, thereby affecting the ice caps, which react slowly to climate forcings because of their large mass. Consequently, the climate system can take centuries, or longer, to respond to climate forcings. Plate tectonics, which reconfigure the oceans and landmass, also play a role in modifying ocean currents and the climate. Depending on the phase relationship of the various forcings, and their feedbacks, the net effect may contribute to warming, cooling or maintaining the status quo.

Variations in solar intensity may have been a factor in the Medieval Warming (from around 900 to around 1200) during which time the Danes colonised Greenland. Following this, the Little Ice Age (from around 1200 to around 1600) saw a cooling in the climate. Solar intensity may also have contributed some of the warming seen from 1900 to 1950. The continued rise in temperature from 1950 to 2000 is thought by some to be continued recovery from the Little Ice Age. These were climate changes, most of which happened long before man could have had an influence, and which could be a result of cyclical solar activity. So far, they remain unexplained.

The cyclical nature of the sun's energy output is seen as the main climate forcing by some scientists. One of the most prominent was Theodor Landscheidt who proposed in his Papers novel ideas about the sun's influence on the planet's climate and successfully predicted the onset of the last El Nino. This included the slow changes within the sun as it ages and evolves, its interactions with the planets in the solar system, and variations from sunspot activity with several cycles from 11 years to several hundreds of years. These are important, as 98% of the heating effect of the planet is from the sun. Sunspot activity changes between periods of high activity, associated with lower energy reaching the planet, and low activity, with increasing energy reaching it. We are now entering a new cycle (cycle 24) with predicted lower than average sunspot activity, which some believe will trigger changes that will last for the next 30 years or so, and could presage a period of global cooling.

Other factors may include increased volcanic activity, (which normally has a short cooling effect) the internal variability of the climate system and anthropogenic effects (human activity).

A measure of climate change, used by many of the scientists working in this field of research, is the reconstructed temperature of the Earth. This is the measure used by the IPCC in its publications, the latest being AR4, referred to above, to illustrate anthropogenic global warming. It is summarised in a chart, which shows a so-called 'hockey stick' temperature record for the past 1,000 years.

This has been questioned, see the Hockey Stick Controversy.
There is an ongoing debate, about the way temperatures have been reconstructed from proxy data. The latest controversy involves the Climatic Research Unit at the University of East Anglia, which has had some private emails, and details of the design of its climate models, released to a wider audience, dubbed 'Climategate'.

Records of surface temperature are available from the late 1800s to the present day, using direct temperature measurements. For earlier periods, all of the evidence is indirect and is inferred from changes in natural phenomena that respond to climate, such as vegetation, ice cores, dendrochronology (the study of tree rings), sea level change, and glacial geology. As a result of recent revelations the UK's Met Office has decided to reexamine 150 years of temperature data and to release it for peer review.

Expressed as a linear trend, the global mean surface temperature rose by around 0.7 degrees over the period 1906-2005. The rate of warming over the last 50 years of that period was almost double that for the period as a whole. The urban heat island effect is estimated to account for about 0.002C of warming per decade since 1900 by some observers. The effects of land usage change is still not totally understood, but some scientists believe it has contributed to increasing the surface temperature.

Temperatures in the lower troposphere have increased between 0.12 and 0.22C per decade since 1979, using satellite temperature measurements. Satellite measurements, although the best we have, are prone to error because of calibration and instrument drift.

The anthropogenic factors studied by scientists include the changes in greenhouse gases, which could increase the earth's temperature by preventing solar energy received from the sun being re-radiated into space. These gases include carbon dioxide in the atmosphere (which is both naturally occurring and from burning fossil fuel, and is less than 1% of the gases in the atmosphere), followed by aerosols (and particulate matter in the atmosphere) and cement manufacture. Other factors, including land use (mentioned above), ozone depletion, animal agriculture and deforestation, which are also considered to be climate change elements.

More about pollution can be found in Atmospheric Pollution from the Internal Combustion Engine in the Urban Environment.

Naturally occurring greenhouse gases have a mean warming effect of about 33C. (Without them we would have frozen to death and plants would not grow and thrive at any temperature). The major naturally occurring greenhouse gases are water vapour, which causes about 36 to 70 percent of the greenhouse effect; carbon dioxide, which causes about 9 to 26 percent; methane, which causes about 4 to 9 percent and ozone, which causes about 3 to 7 percent.

Clouds both affect the radiation received from the sun and prevent it from being re-radiated into space. They are composed of liquid water or ice and are considered separately from water vapour and other gases. See later for more on clouds. This includes the reflectivity of the planet, its albedo, which depends partially on the thickness and extent of clouds.

The oceans release and absorb most of the carbon dioxide in the atmosphere: around 90 gigatonnes (GT) a year. Land sources also contribute a significant portion: around 60Gt. This compares to anthropogenic sources of about 9Gt, which is around 6% of the natural flux. As CO2 is less than 1% of the gases in the atmosphere, anthropogenic CO2 is less than 0.06% of the gases in the atmosphere, and it is argued that this is the main cause of climate change. For more on this see The Carbon Cycle and Atmospheric Carbon Dioxide.

Greenhouse gases and solar forcing affect temperatures in the atmosphere in different ways. While increased solar activity and greenhouse gases are expected to warm the troposphere, an increase in solar activity should warm the stratosphere, see Global Warming for more details. An increase in greenhouse gases should cool the stratosphere. Observations of temperatures of the stratosphere have been cyclical, or falling, since 1979, when satellite measurements first became available. Radiosonde (weather balloon) data from 1958 show cooling, but there is greater uncertainty in these records.

There are, of course, sceptical, some would say dissident scientists, many of whom have written peer-reviewed papers that describe and analyse other climate change science events. They are available here in Sceptical Peer-Reviewed Papers.

Climate Models

The focus of much of the entire scientific endeavour is to develop a reliable climate model, which may be used to predict future climate change and improve our understanding of the climate so that we can modify our behaviour, if necessary, to avoid a catastrophe.

All current-generation climate models are combinations of smaller models that are joined together to make a bigger one. These include an atmospheric model for air movement, and temperature; an ocean model that predicts temperature, salt content, and circulation of ocean currents; a model for ice covers on land and sea and a model of heat and moisture transfer from soil and vegetation to the atmosphere. Some models also include chemical and biological processes.

Climate models predict a warmer climate due to increasing levels of greenhouse gases. But there is some inconsistency in outputs with the same inputs. The representation of clouds is just one of the main sources of uncertainty in present-generation models. The IPCC has stated that 'models continue to display a substantial range of global temperature change in response to specified greenhouse gas forcings. Despite such uncertainties, however, models are unanimous in their prediction of substantial climate warming under greenhouse gas increases, and this warming is of a magnitude consistent with independent estimates derived from other sources, such as from observed climate changes and past climate reconstructions'in AR4, Chapter 8, page 601.
Further discussion of models and their significance is available in,
RealClimate RC11May08.
Quoting from the blog: 'The main result is that 95% of the time, a new record (for temperature, compared with 1998) will be seen within 8 years, but that for an unambiguous record, you need to wait for 18 years to have a similar confidence'.

The Earth's Energy Budget

Energy from the sun has been estimated at 174PW (a Petawatt is ten to the power 15 watts). This is equivalent to 340 W per square metre, which varies by 0.1% over the solar cycle, around 1 W per square metre. Anthropogenic warming has been estimated at 2.4 W per square metre. Of the incident energy, around 30% is reflected by the Earth's albedo and 70% is absorbed and re radiated as infrared. The albedo includes 6% from the atmosphere, 20% from clouds, and 4% from the ground (including ice). The absorbed energy is taken in by the land and water (51%), and atmosphere (19%). Of the 51%, most is sent back into the atmosphere (23%) by the latent heat of evaporation of water, with 7% by heated rising air, 6% radiated directly into space and 15% transferred into the atmosphere by radiation before being re radiated into space. Of the 19% absorbed by the atmosphere and clouds, 16% is re radiated into space and 3% transferred to clouds from where it is re radiated into space.

Science, Politics and Consensus

Science and politics are inter-dependent. Governments need science to advise in formulating policy and scientists need politicians to pay for science. However, science progresses when there is a dissenting view and research funding to back it up. There is no place in science for consensus if it stifles, or undermines dissent. The IPCC, as the main adviser to governments, has a great responsibility to ensure that where there is scientific doubt, it should not be misrepresented. Its claim that there is consensus amongst scientists only applies to scientists' agreement that the climate has been warming over the last 50 years, and not to the reasons for it.

A recent Open Letter from members of the American Physical Society, signed by 160 leading scientists, (and subsequently rejected by its Council), asked that the following proposal be adopted as the official APS stance to government:

'Greenhouse gas emissions, such as carbon dioxide, methane and nitrous oxide, accompany human industrial and agricultural activity. While substantial concern has been expressed that emissions may cause significant climate change, measured or reconstructed temperature records indicate that 20th and 21st century changes are neither exceptional nor persistent, and the historical and geological records show many periods warmer than today. In addition, there is an extensive scientific literature that examines beneficial effects of increased levels of carbon dioxide for both plants and animals.'

See Referenced Sites for the letter and further information about the APS scientists' rejected petition, and in particular their criticism that 'the committee merely consulted existing material contained in IPCC reports (and an accommodating NRC report) and accepted those claims as authoritative. The IPCC claims were in fact the ones countered by the claims in the Open Letter. It makes no mention of consulting the substantial published literature standing in opposition to IPCC positions'.

Many climate scientists state that they are put under pressure to distort or hide scientific results which suggest that human activity is to blame for global warming. See Political Pressure on Scientists.

A US Senate report names 700 scientists, along with their reasons for believing climate change is not man-made, in More Than 700 International Scientists Dissent Over Man-Made Global Warming Claims.

Closing Remarks

The science of climate change is still developing because computer models are not yet able to predict how the climate is changing. Clouds and water vapour, and their impact on the atmosphere, and as feedback mechanisms for climate change, are not well represented in current models.

The climate has changed over time due to many factors, and has been cyclical in its behaviour. These changes have not been fully explained, so far. Studies of natural processes, including ocean and solar cycles, could account for variations in the planet's climate on the timescale of decades and centuries, but is still work in progress.

It is perhaps sensible, in the light of this uncertainty, to try to reduce the anthropogenic element in climate change. We can do this by reducing our emissions of greenhouse gases and by investing in some renewable energy sources (which do not further damage the environment and our economic well-being). However, the pace and cost of those investments needs to be appropriate, and motivated by science and understanding.