This article will be split into two parts, this is part 1 of the article. In a previous article we discussed why the climate varies over time, identifying the main change drivers. We discussed how greenhouse gases trapped the Sun’s heat close to the surface of the planet, while the reflectivity of the Earth’s surface (including the effects of pollution and volcanic activity) reflects heat away.

We discussed how eccentricities in the Earth’s orbit (bringing Earth close to or further from the Sun periodically) and the variation in intensity of solar radiation changes the amount of the Sun’s warmth that reaches the Earth. Finally we discussed how changes in the positions of the land masses alter sea and air currents modifying the temperature directly.

Now let’s look at the global warming discussion itself. Whereas in the previous article we were dealing with high level climatic change drivers which have affected environmental conditions over the 4.5 billion year history of Earth, in this article we are exploring the extent to which people are responsible to recent changes in atmospheric conditions. The dominant side of the global warming debate, loosely, argues that recent economic activity is warming the Earth’s climate and restricting the planet’s natural mechanisms for moderating such changes.

By “recent,” in this article we mean from the fairly arbitrary date of the beginning of the 20th century onwards. This date marks both when people started keeping adequate weather and temperature record and when our population and levels of economic activity became significant enough to have an impact. The Global warming debate includes three components:

• Is there an upward trend in recent global temperature changes?
• Assuming that there is an upward trend is this a result of modern industrialization?
• Assuming that people are to blame for this upward trend how do we respond?

The prevailing point of view in this discussion, by a very significant margin, is that the answer to the first question is yes, to the second is yes, and to the third… well that’s a thorny one.

In response to the first question, the Intergovernmental Panel on Climate Change (established by two organization of the United Nations: the World Meteorological Organization and the United Nations Environment Programme) stated in their “2007: Summary for Policymakers” that:

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

And in response to the second question they say that:

The understanding of anthropogenic warming and cooling influences on climate has improved… leading to very high confidence that the global average net effect of human activities since 1750 has been one of warming…

Elsewhere, in partially addressing the third question, they are more explicit in identifying the causes of their identified warming:

Global atmospheric concentrations of carbon dioxide, methane and nitrous oxide have increased markedly as a result of human activities since 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.

The UK Meteorological office has tracked changes in global temperatures and they have reported that global temperatures have risen by 0.75 degrees over the last 100 years. Since 1960, carbon dioxide [CO2] levels in the atmosphere, as measured by the Mauna Loa Observatory (operated by the United States Climate Monitoring and Diagnostics Laboratory), have increased from just below 320 part per million to over 380 parts per million (with some reports suggesting that levels of CO2 were as low as 280 ppm in preindustrial 1750).

So what is happening here? Well, over a short period the climate is affected by the quantity of greenhouse gases in the atmosphere, the earth’s albedo (ie how much of the sun’s energy it absorbs or reflects), the amount of aerosols (small particles) in the atmosphere, and finally (if controversially) the amount of radiation emitted by the Sun.