Climate change: the big picture

The Geological Society of London recently published a position statement which with articulacy and precision outlines the science of climate change in little more than six pages of text. The statement contains a fair amount of scientific jargon, much of it defined, and demands a careful reading rather than a cursory glance.

What is particularly valuable about the Geological Society’s statement is that it sets contemporary climate change in a pre-historical context and global timeline, discussing both natural and human influences on the Earth’s climate. For example, our planet’s distant past saw climate change far greater than is predicted arising from anthropogenic emissions of carbon dioxide. The difference today is that the Earth now carries a human population numbered in the billions, many of whom live in coastal regions at risk from sea level rise, or on land the fertility of which is highly sensitive to changes in temperature and precipitation.

“Global sea level is very sensitive to changes in global temperatures. Ice sheets grow when the Earth cools and melt when it warms. Warming also heats the ocean, causing the water to expand and the sea level to rise. When ice sheets were at a maximum during the Pleistocene, world sea level fell to at least 120m below where it stands today. Relatively small increases in global temperature in the past have led to sea level rises of several metres. During parts of the previous interglacial period, when polar temperatures reached 3-5°C above today’s, global sea levels were higher than today’s by around 4-9m. Global patterns of rainfall during glacial times were very different from today.”

The statement goes on to explain how the carbon dioxide level has risen by a third in the past 200 years (i.e., since the start of the industrial revolution), with over half of the increase occurring during the last 30 years. There is evidence to suggest that this rise is comparable with the abrupt global warming during the Early Jurassic period, 183 million years ago, and also the Paleocene-Eocene Thermal Maximum of 55 million years past. And we know from the geological record what happened to sea levels and vegetation cover during those times.

“While these past climatic changes can be related to geological events, it is not possible to relate the Earth’s warming since 1970 to anything recognisable as having a geological cause (such as volcanic activity, continental displacement, or changes in the energy received from the sun).”

The language may be sober, but the conclusions drawn by the learned geologists are every bit as stark as those of model crunching atmospheric physicists and chemists, and environmentalists and policy wonks responsible for drafting the climate change narrative for public consumption. I urge you to read the full statement for yourselves.

Further reading: “Climate change: evidence from the geological record”, The Geological Society, November 2010