Skip to main content

Paul F. Hoffman visits the University of Bristol



Paul F Hoffman of Harvard
On the 24th and 25th of September, Professor Paul F Hoffman of Harvard University (USA) kindly offered to visit the University of Bristol for two days. Fresh from fieldwork in Namibia, Paul agreed to give two talks: one upon Cryogenian glaciations and another upon the interaction of climate scientists and geologists.

Snowball Earth - Image from COSMOS
Paul is perhaps most well known for his part in the development of the Snowball Earth theory, suggesting that during the Cryogenian (850 to 635 million years ago) ice covered the entire globe, from the poles to the tropics. This theory is based upon multiple strands of evidence including palaeomagnetics, sedimentology, isotopic analysis and numerical modelling. Paul succinctly summarised these ideas while also discussing some new results published in Science two years ago. The authors of this paper suggest that during the breakup of Rodinia, a proterozoic supercontinent, the eruption of the Franklin Large Igneous Province (LIP) in Canada (716Ma) may have produced a climatic state more susceptible to glaciation. Although there have been many critics of Snowball Earth, it seems Paul remains loyal to the theory.  A wine reception was held afterwards within the School of Geography and allowed for further discussion amongst staff and students.

Paul gave a second talk on 25th September to a selection of PhDs and PDRAs who attend the Climate Journal Club (see below for details). Paul chose to give a more anecdotal, but nonetheless interesting, talk on the co-evolution of climate scientists and geologists during the last 250 years. His talk focused upon the development of a theory: from indifference to hysteria, followed by rejection and then finally acceptance. I asked him where Snowball Earth stands. He replied that it was somewhere in between hysteria and rejection!

Maybe in 50 years time we will know whether Paul was right all along...

--------------------------------------------------------------------------
For more details, see the following references:

Hoffman, P.F., et al (1998) A neoproterozoic Snowball Earth. Science, 281, 1342
MacDonald, F.A., et al (2010) Calibrating the Crypogenian. Nature, 327, 1241

This blog was written by Gordon Inglis who runs the Climate Journal Club at the University of Bristol. 

For more details on attending the Climate Journal Club (bimonthly event designed to allow PhD and PDRAs to discuss a selection of climate-themed paper), please email Gordon.Inglis@bristol.ac.uk

Popular posts from this blog

Converting probabilities between time-intervals

This is the first in an irregular sequence of snippets about some of the slightly more technical aspects of uncertainty and risk assessment.  If you have a slightly more technical question, then please email me and I will try to answer it with a snippet. Suppose that an event has a probability of 0.015 (or 1.5%) of happening at least once in the next five years. Then the probability of the event happening at least once in the next year is 0.015 / 5 = 0.003 (or 0.3%), and the probability of it happening at least once in the next 20 years is 0.015 * 4 = 0.06 (or 6%). Here is the rule for scaling probabilities to different time intervals: if both probabilities (the original one and the new one) are no larger than 0.1 (or 10%), then simply multiply the original probability by the ratio of the new time-interval to the original time-interval, to find the new probability. This rule is an approximation which breaks down if either of the probabilities is greater than 0.1. For example

1-in-200 year events

You often read or hear references to the ‘1-in-200 year event’, or ‘200-year event’, or ‘event with a return period of 200 years’. Other popular horizons are 1-in-30 years and 1-in-10,000 years. This term applies to hazards which can occur over a range of magnitudes, like volcanic eruptions, earthquakes, tsunamis, space weather, and various hydro-meteorological hazards like floods, storms, hot or cold spells, and droughts. ‘1-in-200 years’ refers to a particular magnitude. In floods this might be represented as a contour on a map, showing an area that is inundated. If this contour is labelled as ‘1-in-200 years’ this means that the current rate of floods at least as large as this is 1/200 /yr, or 0.005 /yr. So if your house is inside the contour, there is currently a 0.005 (0.5%) chance of being flooded in the next year, and a 0.025 (2.5%) chance of being flooded in the next five years. The general definition is this: ‘1-in-200 year magnitude is x’ = ‘the current rate for eve

Coconuts and climate change

Before pursuing an MSc in Climate Change Science and Policy at the University of Bristol, I completed my undergraduate studies in Environmental Science at the University of Colombo, Sri Lanka. During my final year I carried out a research project that explored the impact of extreme weather events on coconut productivity across the three climatic zones of Sri Lanka. A few months ago, I managed to get a paper published and I thought it would be a good idea to share my findings on this platform. Climate change and crop productivity  There has been a growing concern about the impact of extreme weather events on crop production across the globe, Sri Lanka being no exception. Coconut is becoming a rare commodity in the country, due to several reasons including the changing climate. The price hike in coconuts over the last few years is a good indication of how climate change is affecting coconut productivity across the country. Most coconut trees are no longer bearing fruits and thos