What does this all mean for human induced climate change?

Values of carbon dioxide have been rising steadily in the atmosphere since instrumental records began in 1960 (Figure 1). This is related to the emission of greenhouse gases via the anthropogenic burning of fossil fuels. If we continue to emit greenhouse gases under a ‘business-as-usual’ scenario (i.e. no mitigation and continued economic expansion), the earth’s climate may reach temperatures and pCO2 concentrations comparable to the early Eocene greenhouse. Therefore it is key that we understand the ‘greenhouse ‘climate of the early Cenozoic in much greater detail.

Figure 1. It shows the longest record of direct measurements of CO2 in the atmosphere in red while the black curve represents the seasonally corrected data[1].

Although the scenarios derived by the 4th IPCC report do not offer a crystal ball for the future, they do yield valuable insights into the interaction of natural and human-induced climate processes. In order to improve our current climate models, they need to be tested against time periods when the Earth was warmer than today.  In order to this however we need to understand the past climate in greater detail than we currently do.  In particular we need to know how warm it was, the pattern of the warmth and its cause (e.g. was CO2 2000 ppm or 5000 ppm?).  The ‘Descent into the Icehouse’ project aims to provide such palaeoclimatic data for testing the next generation of climate models (http://descentintotheicehouse.org.uk/?p=633)

Figure 2. It shows a range of emission scenarios related to anthropogenic climate change and the resulting rise in global surface temperature (between 2-6°C) (left) and the regional temperature response related to three different scenarios (A2, A1B and B1) (right)[1]

[1] Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.), 2007, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press