[Lucky Dog]

If we do not slow down the rate of global warming, many species are likely to become extinct. In effect we are pushing them off the planet.

Author’s implied logic chain:

Premise: The earth’s climate is becoming warmer than it should from natural processes.
Premise: This warming is the result of human activity.
Conclusion: Changing human activity will stop global warming.

This syllogism is invalid as well as unsound from a number of perspectives. First, the major premise contains an unproven assumption that the current postulated warming is not part of a natural statistical variation. Second, the minor premise is unproven and, hence, the conclusion is potentially false. Third, the conclusion is not inevitable as, even if the second premise were true, it may be too late to reverse any trend or, perhaps, a natural mechanism will mitigate the situation such as a increase in plant life (like algae) to absorb and convert CO2 or other green house gases.

Author’s implied logic chain:

Premise: Global warming is bad.
Premise: Changing human activity will stop global warming.
Conclusion: Prudence demands implementing this change immediately.

This syllogism is also invalid and unsound from a number of perspectives. First, as noted above, there is no concrete indication that global warming will lead to catastrophic or deleterious effects. In fact, ice core drillings have indicated that the earth has been warmer as well as cooler than it is now a number of times in the past without catastrophe. Second, the minor premise is faulty as noted above. Finally, the conclusion ignores the deleterious impacts on humanity of the proposed changes that are speculated to mitigate the problem without the proof that the proposed changes would do anything to lessen global warming.

[cogitator]

First, the major premise contains an unproven assumption that the current postulated warming is not part of a natural statistical variation.

There are many indications that the current warming trend is not due to natural variation (primarily).

Conclusion: Changing human activity will stop global warming.

Hansen is actually a believer in alternate energy and new technology as the best way to address the situation.

Conclusion: Prudence demands implementing this change immediately.

Hansen has expressed the viewpoint that humanity, collectively, has a decade or so to start doing something substantial about global warming or irreversible changes with the potential to induce significant-to-severe climate alteration in the future will become much more probable.

In fact, ice core drillings have indicated that the earth has been warmer as well as cooler than it is now a number of times in the past without catastrophe.

Define "catastrophe" in this context. For the glacial-interglacial era, there have only been a few short periods during prior interglacials that were slightly warmer than now -- without the higher CO2 concentrations in the atmosphere that will contribute to even higher temperatures. So the Earth may be on the verge of entering an unprecedented climate state.