As an example sea level rise was initially forecast to be in the range of 300mm to 900mm and now we are looking at up to 2200mm by the end of the century and that is without the collapse of the West Antarctic.
The problem has always been the lack of knowledge and the provable ramifications of change. Knowing the that Antarctic ice sheet has enough ice to raise sea levels by 60 metres means very little if it is going to take 1000 years. What we need to know is when are we going to get a sea level rise that will flood Aukland airport and cut Northland off from the rest of the country? Is it in the lifetime of our children or our grandchildren or is it sometime in the distant future?
The point we are reaching now is putting a scale to the sensitivity of the planet which can then express the outcome in time.
There are many scientists working on various aspects of climate change but Professor James Hansen, who is an atmospheric scientist, has been measuring various sudden planetary events, such as volcanoes, to measure the reaction of the planet to the sudden input of dust or water and the time it takes to recover to estimate the sensitivity of the planet.
His work on the sudden elimination from the atmosphere of sulphur by ships burning cleaner fuel is a measurable event and we have seen that sulphur has reduced from 11 million tonnes a year down to 2.5 million tonnes. The resulting measure of the suns heat to the planet from lower sulphur aerosols might be as high as 0.5 Watts per square metre, which is far higher than the current estimates of 0.05-0.15 Watts per square metre.
The current theory on the effects of the greenhouse gas CO2 is that a doubling of CO2 from 280 PPM to 560 ppm ppm ( we are currently at 427 ) would result in a temperature increase of 3C above 1880 levels while Hansen and colleagues say the increase would be 50% higher at 4.5C.
This is a very worrying scenario and there will be a lot of work done by the scientific community to prove or disprove his work.
At the moment we are due to hit an increase of 3.1C by 2100 but if the planet is 50% more sensitive than current IPCC projections then we could breach 3C by 2075 which is only 50 years away.
3C is a disastrous level of extra heat as it would mean a collapse of food production just as the worlds population is expected to reach 10 billion people. Not a good scenario.