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IPCC: Climate Change Report Summary (Part 1)

The report by the Intergovernmental Panel on Climate Change (IPPC) "describes progress in understanding of the human and natural drivers of climate change and the processes, attribution and estimates of future climate change". By 'Climate Change', the IPCC refers to "any change in climate over time, whether due to natural variability or as a result of human activity".

It is designed to "build upon past IPCC assessments and incorporates new findings from the past six years of research", based upon "large amounts of new and more comprehensive data".

Here is what the IPCC report has to say about the human and natural drivers of climate change:

"Changes in the atmospheric abundance of greenhouse gases and aerosols, in solar radiation and in land surface properties alter the energy balance of the climate system. These changes are expressed in terms of radiative forcing, which is used to compare how a range of human and natural factors driver warming or cooling influences on global climate. "

'Radiative forcing' is not a term that many people are familiar with. The IPCC describes radiative forcing as "a measure of the influence that a factor has in altering the balance of incoming and outgoing energy in the Earth-atmosphere system and is an index of the importance of the factor as a potential climate change mechanism".

Relative forcing is expressed in watts per square metre. The higher the value, the more of a warming influence is being described. Values below zero indicate cooling influences. Therefore, warming influences are described as 'positive forcing' and cooling influences as 'negative forcing'.

Greenhouse Gasses

"Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since (the year) 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. The global increases in carbon dioxide concentration are due primarily to fossil fuel use and land-use change, while those of methane and nitrous oxide are primarily due to agriculture. "

Carbon dioxide, methane and nitrous oxide are the main gases responsible for global warming. It can be seen from the statement above that reducing fossil fuel use and changing the way we use land will reduce most of the carbon dioxide increases in the atmosphere. It can also be seen that changes to agricultural methods could reduce methane and nitrous oxide emissions.

The report goes on to say, "Carbon dioxide is the most important anthropogenic greenhouse gas". Carbon dioxide levels have risen from 280 parts per million (ppm) in pre-industrial times to 379 ppm in 2005. The 2005 level exceeds natural carbon dioxide levels seen in the atmosphere for the last 650,000 years (which was determined from ice-cores). "The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land use change providing another significant but smaller contribution. " Note that 'parts per million' (ppm) means the "ratio of the number of greenhouse gas molecules to the total number of molecules of dry air. For example: 300 ppm means 300 molecules of greenhouse gas per million molecules of dry air".

Similar patterns apply to methane (which has increased from a pre-industrial level of 715 parts per billion (ppb) to 1774ppb in 2005) and nitrous oxide (270ppb to 319 ppb). Methane levels, like carbon dioxide levels, are at their highest level for 650,000 years.

Global Warming caused by Humans

The IPCC report states "The combined radiative forcing due to increases in carbon dioxide, methane, and nitrous oxide is +2.3 watts per square metre, and its rate of increase during the industrial era is very likely to have been unprecedented in more than 10,000 years. The carbon dioxide radiative forcing increased by 20% from 1995 to 2005, the largest change for any decade in at least the last 200 years. " Note that the IPCC uses the term very likely to describe a probability of greater than 90%.

This means that humans are currently adding 2.3 watts per square metre of heat energy to the atmosphere.

Global Dimming caused by Humans

"Anthropogenic contributions to aerosols (primarily sulphate, organic carbon, black carbon, nitrate and dust) together produce a cooling effect, with a total direct radiative forcing of -0.5 watts per square metre and an indirect albedo forcing of -0.7 watts per square metre. Aerosols also influence cloud lifetime and precipitation. "

Humans are blocking out sunlight with aerosols, which causes a cooling effect on the atmosphere.

Net Warming caused by Humans

"The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR), leading to very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming, with a radiative forcing of +1.6 watts per square metre. "

The total warming effect caused by humans, minus the cooling effect caused by humans leads to a net increase of heat energy of +1.6 watts per square metre.

The Effects of Climate Change

The following statements were made as part of the report:

"Warming of the climate system is unequivocal, as is now evident from observations of increases in global air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level".

"Eleven of the last twelve years (1995-2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). "

"The average atmospheric water vapour content has increased since at least the 1980s over land and ocean as well as in the upper troposphere. The increase is broadly consistent with the extra water vapour that warmer air can hold. "

"Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000m and that the ocean has been absorbing more than 80% of the heat added to the climate system. Such warming causes seawater to expand, contributing to sea level rise. "

"Mountain glaciers and snow cover have declined on average in both hemispheres. Widespread decreases in glaciers and ice caps have contributed to sea level rise. "

"New data now show that losses from the ice sheets of Greenland and Antarctica have very likely contributed to sea level rise over 1993 to 2003. Flow speed has increased for some Greenland and Antarctic outlet glaciers, which drain ice from the interior of the ice sheets. "

"Global average sea level rose at an average rate of 1.8 mm per year over 1961 to 2003. The rate was faster over 1993 to 2003, about 3.1mm per year."

"At continental, regional, and ocean basin scales, numerous long-term changes in climate have been observed. These include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones (including hurricanes and typhoons)."

"Average Arctic temperatures increased at almost twice the global average rate in the past 100 years. Arctic temperatures have high decadal variability, and a warm period was also observed from 1925 to 1945. "

"Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 2.7% per decade, with larger decreases in summer of 7.4% per decade. "

"Temperatures at the top of the permafrost layer have generally increased since the 1980s in the Arctic (by up to 3°C). The maximum area covered by seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900, with a decrease in the spring of up to 15%."

"Long term trends from 1900 to 2005 have been observed in precipitation amount over many large regions. Significantly increased precipitation has been observed in eastern parts of North and South America, northern Europe and northern and central Asia. Drying has been observed in the Sahel, the Mediterranean, southern Africa and parts of southern Asia."

"Changes in precipitation and evaporation over the oceans are suggested by freshening of mid and high latitude waters together with increased salinity in low latitude waters." (This is because less solar energy is required to evaporate fresher water, but more solar energy is required to evaporate saltier water, leading to more rain in areas surrounded by fresher seas (mid and high latitudes) and less rain in areas surrounded by saltier seas (equatorial areas).)

"Mid-latitude westerly winds have strengthened in both hemispheres since the 1960s."

"More intense and longer droughts have been observed over wider areas since the 1970s, particularly in the tropics and subtropics."

"The frequency of heavy precipitation events has increased over most land areas, consistent with warming and observed increases of atmospheric water vapour."

"Widespread changes in extreme temperatures have been observed over the last 50 years. Cold days, old nights and frost have become less frequent, while hot days, hot nights, and heat waves have become more frequent."

"There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases of tropical sea surface temperatures." (Tropical cyclones include hurricanes).