Climate Change: the IPCC View

For a biblical perspective see: Is God Changing Our Climate?

Recent Global Warming

Is global warming really happening? The official scientific answer is 'yes'. Figure 1 shows global average temperatures as compiled by the NASA's Goddard Institute for Space Studies (GISS). Data is from surface air measurements at meteorological stations and from ship and satellite sea surface temperature (SST) measurements. The zero on this figure is the mean temperature from 1961-1990.

The GISS also claim "the January-November 2010 surface temperature anomalies are the warmest (along with 2005) in their 131 year analysis period" and that "global warming amounts to 0.8°C over the past century, with the largest warming in remote regions including high latitudes". A 0.8°C rise is also reported by the University of East Anglia Climate Research Unit.

The UK Met Office reports that "the UK has experienced nine of the 10 warmest years on record since 1990". They admit that global temperature rise virtually stopped during 2000 - 2010, but state that this is not regarded as an end to warming - see UK Met Office.

What of the IPCC? The Intergovernmental Panel on Climate Change (IPCC) is a scientific intergovernmental body comprised of two organizations of the UN. It's main activity is to provide regular reports of the state of knowledge on climate change. It is claimed that the core climate science was written by 152 scientists from more than 30 countries and reviewed by more than 600 experts. The 2007 IPCC Report stated that "World temperatures could rise by between 1.1 and 6.4°C during the 21st century".

Other evidence of warming: Sea levels have been rising and glaciers have been retreating since about 1850 (Fig.2, Fig.3). Malaria has spread to higher altitudes and at least 279 species of plants and animals are moving closer to the poles.

Climate Modelling and Prediction

Climate models are mathematical representations of the interactions between the atmosphere, oceans, land surface, ice and the sun. They are the basis for predictions of future climate, and are incorporated into all IPCC Reports. The UK Met Office model HadCM3 was used in the IPCC Third Assessment Report (2001) and model HadGEM1 used in the IPCC Fourth Assessment Report (2007). It is claimed these models give good simulation of current climate. Another model (Hansen et al, 2006) is shown in Fig.4 for several world scenarios. Intermediate scenario B was described as "the most plausible" and correlates well with measured data.

The modelling in Fig.5 (Meehl et al, 2004) is claimed to represent the consensus view on warming. Specifically, it suggests that the natural variations of solar and volcanic activity cannot on their own account for warming. And man-made sulfate emmissions actually reduce global temperature. It is claimed that the model is only able to simulate the temperature record over the past century when greenhouse gases (GHGs) are included in the model. This suggests that GHG increase is crucial to the warming process. This concept is backed by ice-core studies which show that during at least the past 600,000 years (assuming conventional dating methods) carbon dioxide (CO2) levels appear to correlate with temperature variation in the sense that CO2 has been high during warm periods and low during cool periods (see Past Climate Change). Note: a detailed analysis (Zbigniew Jaworowski) throws doubt on this correlation.

Model predictions of future temperature rise depend upon estimates of future GHG emmissions and typically give a rise of 2-5 degree C relative to 1990 levels by 2100 (Fig.6). A 5 degree rise is equivalent to the change in mean temperature from the last ice age to today!

GHGs and Anthropological Warming

The major GHG concentrations are about 7600 ppm for water vapour, 390 ppm for CO2, and 1780 ppb for methane (CH4) (ppm = parts per million by volume, ppb = parts per billion by volume). Ozone and Nitrous Oxide have smaller concentraions. It is claimed that these translate to a greenhouse warming effect of 36-70% for water vapour, 9-26% for CO2, and 4-9% for CH4. Note that CH4 is about eighty times stronger as a greenhouse gas than CO2, but it is present in much smaller concentrations.

Figure 7 shows that CO2 has had a cyclic variation (period approximately 100,000 years) and the graph peaks correspond to interglacial periods. This natural climatic variation may be due in part to the 100,000 year period of the eccentricity of the earth's orbit (Milutin Milankovitch).

The significant point in Fig.7 is that each peak in the cycle levelled at approximately 278 ppm until the industrial revolution around 1800. Since then, the CO2 level has increased dramatically, reaching 390 ppm in 2010! This recent 40% increase in atmospheric CO2 appears to be a sudden departure from the natural variation, with the implication that human activity is responsible for global warming. The IPCC therefore calls this 'anthropogenic warming' (anthropogenic CO2 is that portion of CO2 in the atmosphere that is produced directly by human activities). Moreover, assuming different levels of human economic development, population growth, and fossil-fuel use, IPCC predictions for atmospheric CO2 levels lie between 500ppm and 900ppm by 2100!

Climate sceptics claim solar irradiance is the main driving force for increasing temperatures, not CO2. This claim is countered by the UK Met Office: "Changes in solar activity do affect global temperatures, but research shows that, over the last 50 years, increased greenhouse gas concentrations have a much greater effect than changes in the Sun's energy".

The Consequences

According to adherents of the IPCC view, the physical consequences of warming are catastrophic: e.g. increased drought, flooding, and severe storms. Gulf Stream slow-down could plunge the USA and NW Europe into cold and drought. The social consequences are summarised in a few key reports:

The Global Warming Controversy

The IPCC position on global warming is that concentrations of certain greenhouse gases have dramatically increased due to the burning of fossil fuels and deforestation and that this probably accounts for most of the warming over the past 50 years. Certainly, carbon emissions have increased dramatically since 1950 (Fig.8). The IPCC also claims that the majority of climate scientists agree with this position and that it has been endorsed by more than 50 scientific societies and academies of science. Challenges to this theory from climate sceptics are dismissed in Skeptical Science and by offical bodies like the The Royal Society.

Also, the UK Met Office state: "It is now clear that man-made greenhouse gases are causing climate change".

On the other hand, tens of thousands of scientists dispute the IPCC claim and have signed the Global Warming Project Petition. Why?

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