Date: Tuesday, 7 July 2009, 6.00pm
Venue: Hunter Building Lecture Theatre 323
I couldn't make this lecture, but my brother Jonathan did. Here are his notes:
What caused the increase in atmospheric carbon dioxide 4 million years ago?
We are not completely sure why atmospheric carbon dioxide increased from about 300ppm to 400ppm between 5 and 3 million years ago. We do know that it happened over about 1-2 million years unlike the recent increase to 400ppm which happened in the last 150 years. We suspect it was due to long term changes in Earth’s carbon cycle due to geological processes. An enduring theory is that it is to do with uplift of the Tibetan Plateau which began about 10 million years ago and finished about 3 million years ago. Also at 3 million years ago the Panama Seaway closed through plate tectonic processes. Atmospheric and ocean circulation processes changed. We suspect that increased precipitation associated with uplift of the Himalayas lead to acid rain dissolving silicate rocks producing carbon dioxide.
Is the increase in atmospheric carbon dioxide since 1850 human-induced?
Yes. This fact is accepted by sceptics and IPCC climate scientists alike. We know the measured increase in CO2 since 1950 is from fossil fuel burning, not volcanic eruptions or oceanic methane. We also measure a corresponding decrease in the atmospheric nitrogen/oxygen ratio indication that oxygen is being consumed as fossil fuels are burned. No known natural processes can account for this 30% increase above highest levels known for the last 2 million years.
If it happened in the past naturally why should we be worried about the recent increase in atmospheric carbon dioxide over the last 150 years?
This is a question I commonly get asked. It’s actually a red-hearing as to how atmospheric carbon dioxide increased in the last 150 years. I notice with many people there is this denial factor - that so what if we did it…it happened in the past by natural processes anyway! The point is…Yes it did happen 4 million years ago, and we know Earth’s average temperature increased by ~4°C and probably 7-8 °C in the Polar Regions. During this time Greenland and West Antarctic Ice Sheets were highly unstable and deglaciated numerous times raising sea-level by more than 20ms above present. That is the key point. Also our predecessors (Australopithecus) were quite primitive. Our society/civilisation today is highly sophisticated and we have a lot more to lose. That's why the past is so important when planning for the future. The prospect of some of the changes we see in the past happening even within the next 100 years will have major impacts on our civilisation ( sea-level rise, extreme climate events, changes in mean climate, water security, energy security, disease, famine). Add to this that the human-induced rise in atmospheric carbon dioxide is happening at an unprecedented rate compared to 4 million years ago and we might expect some impacts to occur significantly faster than they did in the geological past. There is no question that the human imprint is going to commit us to climate change in the next century. And yes the Earth will remediate itself. It always does. But over thousands of years and always with major “adjustments” to the ecosystems that existed beforehand.
The ecological niche presently occupied by humans is under extreme pressure over and above climate change (in fact climate change is consequence of other factors). Our species has over-exploited the available resources of planet Earth. With population increase from 1 billion in 1900 expected to top out near 9 billion by 2050 there simply are not enough resources to sustain our present civilisation. Our unsustainable behaviour will cause devastating changes to our way of life probably before climate change does. Within decades water availability and oil supplies will cause fundamental changes to our economies and societies. Competition for limited resources exacerbated by climate change will lead to significant lose of life through war, disease and food shortage.
Whether its peak oil or climate change that brings governments to the negotiating table to work collectively to reduce our dependence on fossil fuels this will be a 1st order step towards a more sustainable future where the wants of the individual are balanced against the needs of our collective societies to provide a long term security and sustainability.