The Intergovernmental Panel on Climate Change (IPCC)



The IPCC have issued three Summary Assessment Reports; the first in 1990 and the second in 1995 that provided key input to the negotiations leading to the adoption of the Kyoto Protocol in 1997.

The Third Assessment Report was completed in 2001, from which the text on this page has been taken. With another six years of continued observation and research and greatly improved computing power and climate models, the Third Assessment Report makes pretty convincing reading that Climate Change is a reality.

Now that the Summary of the Fourth Assessment Report has been released, it's pretty clear that we're already heading for trouble. We'd better get some changes happening..

Climate Changes so far

The global average surface temperature (the average of near surface air temperature over land, and sea surface temperature) has increased since 1861. Over the 20th century the increase has been 0.6 ± 0.2°C. In the mid- and high latitudes of the Northern Hemisphere over the latter half of the 20th century, it is likely that there has been a 2 to 4% increase in the frequency of heavy precipitation events.

On average, between 1950 and 1993, night-time daily minimum air temperatures over land increased by about 0.2°C per decade. This has lengthened the freeze-free season in many mid- and high latitude regions. There has been a widespread retreat of mountain glaciers in non-polar regions during the 20th century. Northern Hemisphere spring and summer sea-ice extent has decreased by about 10 to 15% since the 1950s.

Tide gauge data show that global average sea level rose between 0.1 and 0.2 metres during the 20th century. Global ocean heat content has increased since the late 1950s.

Global Gases

The atmospheric concentration of carbon dioxide (CO2) has increased by 31% since 1750. The present CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years.

About three-quarters of the anthropogenic (caused by humans) emissions of CO2 to the atmosphere during the past 20 years is due to fossil fuel burning. The rest is predominantly due to land-use change, especially deforestation.

The atmospheric concentration of methane (CH4) has increased by 1060 ppb (151%) since 1750 and continues to increase. The present CH4 concentration has not been exceeded during the past 420,000 years.

Natural Climate Factors

Natural factors have made small contributions to radiative forcing over the past century. The combined change in radiative forcing of the two major natural factors (solar variation and volcanic aerosols) is estimated to be negative for the past two, and possibly the past four, decades. In other words, variability in solar irradiance and volcanic eruptions do not explain the warming in the second half of the 20th century.

Climate Models are Getting Better




The Findings

The Second Assessment Report concluded: The balance of evidence suggests a discernible human influence on global climate. Since then, progress has been made in reducing uncertainty, particularly with respect to distinguishing and quantifying the magnitude of responses to different external influences. Although many of the sources of uncertainty identified in the SAR still remain to some degree, new evidence and improved understanding support an updated conclusion.

There is a longer and more closely scrutinised temperature record and new model estimates of variability. The warming over the past 100 years is very unlikely to be due to internal variability alone, as estimated by current models. Reconstructions of climate data for the past 1,000 years also indicate that this warming was unusual and is unlikely to be entirely natural in origin.

The warming over the last 50 years due to anthropogenic greenhouse gases can be identified despite uncertainties in forcing due to anthropogenic sulphate aerosol and natural factors (volcanoes and solar irradiance). Changes in natural forcing during most of this period are also estimated to be negative and are unlikely to explain the warming.



As Henry Porter observed at the Climate Change Conference in 2005, "Even the scientists were shocked by how advanced various manifestations of global warming were."

Dangerous climate change is on our doorstep. When will we acknowledge the experts?

We need radical action starting yesterday.