I haven't looked closely at the issue of species extinction yet but Hansen and other research convinces me that the threat of rising sea levels is real and that the IPCC estimates are conservative. Sea level rise is difficult for humans to adapt to since so many people and important cities are located around the coastline. I hadn't thought about this much before. I had thought that Climate might or might not be changing but the IPCC maximum projection of 59cm in the next century was a maximum and was sufficiently far off in the future to be not a major problem.
Hansen points out that sea level stability has been with us for approximately 7,000 years and that this provided enormous advantages for the emergence of civilisation, such as increased fish breeding around the coasts providing a high protein diet for a settled population. He also uses paleoclimate data to point out that in the previous interglacial, the Eemian, 140,000 years ago, at one stage the climate was only 1 degree Celcius warmer and the sea level was 4-6 metres higher. See Fig. 3 (source)
My thinking was guided by the idea that everything changes continually anyway and in general new technological discoveries can be used to overcome new problems as they arise. I still think this is correct as a generalisation but I can't think of anyway in which new technologies would overcome a significant sea level rise for millions of people. Of course, it's possible / probable that sea level will rise anyway, sooner or later, and we will have to adapt. But it seems that we have reached the point where we do have some control over the climate and should collectively exercise that control.
Back to the present, the evidence from the GRACE satellites (Gravity Recovery and Climate Experiment) and other data indicates that the ice sheets in Antarctica (especially West Antarctica) and Greenland are losing mass at an accelerating rate. The GRACE figures are in gigatonne per year and the mass loss is accelerating over the period measured (2002-09) on both sheets:
In Greenland, the mass loss increased from 137 Gt/yr in 2002–2003 to 286 Gt/yr in 2007–2009, i.e., an acceleration of −30 ± 11 Gt/yr2 in 2002–2009. In Antarctica the mass loss increased from 104 Gt/yr in 2002–2006 to 246 Gt/yr in 2006–2009, i.e., an acceleration of −26 ± 14 Gt/yr2 in 2002–2009.A central issue is the inertia of the oceans and the ice sheets. Ice begins to melt slowly but the rate accelerates over time. Ice in the wild has different dynamics. Ice flows, ice can get dirty, moulins can form to accelerate the destruction etc. With oceans the warming process is much slower overall but the quicker part is early rather than late. These combined inertias create the threat that if you go past a tipping point, which we can’t predict, then you can’t recover from it. We may be letting systems which are controllable to an extent slip out of control. With so many people living in coastal regions then anything faster than the IPCC predictions would be a real concern for future generations.
I still think that economic and industrial development is very important for everyone, especially for the developing world. Since we have the nuclear energy option I don't see any reason for pessimism about the long term energy future for humans. However, the present problem is that nuclear is more expensive and subject to excessive regulation owing to the widespread fear of anything nuclear. These issues have been and are being discussed in detail at Barry Brook's blog, Brave New Climate.
At the moment I'm particular interested in the threat of rising sea levels. I found another excellent blog, Getting skeptical about global warming skepticism which has a series of posts about this question. This amazing page lists 94 skeptical arguments and links to responses to all of them based on reviews of peer reviewed papers by John Cook, a Queensland physicist. Here are some of the links to Cook's blog which directly or indirectly look at the issue of rising sea levels:
Sea levels aren't rising
Ice isn't melting
How much will sea levels rise in the 21st Century?
Is Greenland gaining or losing ice?
It's the ocean
Arctic ice melt is a natural cycle
Does ocean cooling prove global warming has ended?
Reading these references makes me think that the IPCC maximum estimate is a conservative one and the sea level may well rise faster than that. This video provides an illustration of how the ice sheet dynamics might work, explains the reasons for IPCC conservatism and looks at some of the paleoclimate data. The section right at the end is overly alarmist but overall it's worth watching: