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Re: The planet's future: Climate change 'will cause civilisation to collapse'
Ok, here goes. Global temperatures went up by 0.6 degrees during the twentieth century, and there was no noticeable impact. We were too busy fighting wars and chopping down the forests to notice.
Given likely trends in CO2 emissions, global temperatures will probably rise another 0.6 degrees during the 21st century. Again, by 2099 there will probably be other much more important threats monopolising our attention, and the impact will not be noticeable.
During the 20th century, the human population of this planet went from 1.5 billion to 6 billion, accompanied by enormous habitat destruction and the extinction of many species. That's the real threat to the environment, not a 0.6 degree rise in average temperatures.
As far as natural variability goes - over the last 130 years we can see a 60 year cycle at work. Temperatures declined slightly from 1880 to 1910, then rose from 1910 to 1940, then declined from 1940 to 1970, then rose from 1970 to about 2000, and have declined slightly since.
So we are looking at a 130 year uptrend superimposed over a 60 year natural fluctuation. We can expect temperatures to be flat until around 2030, before starting another upleg into 2060.
Now obviously the 60 year cycle is natural. Now that it is obvious it is being explained in terms of PDO. The question is, does the longer 130 uptrend represent AGW, or another natural cycle with a longer period, or contributions from both?
The short answer is "we don't know - yet". The magnitude of the change is about right if a doubling of CO2 leads to a 1 degree temperature rise, and the positive and negative feedback cancels out.
But a change of that size could also be explained by natural variability - a cursory glance at the temperature record for the last 4000 or 4 million years should show that there is no real stability.
Originally posted by we_are_toast
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Given likely trends in CO2 emissions, global temperatures will probably rise another 0.6 degrees during the 21st century. Again, by 2099 there will probably be other much more important threats monopolising our attention, and the impact will not be noticeable.
During the 20th century, the human population of this planet went from 1.5 billion to 6 billion, accompanied by enormous habitat destruction and the extinction of many species. That's the real threat to the environment, not a 0.6 degree rise in average temperatures.
As far as natural variability goes - over the last 130 years we can see a 60 year cycle at work. Temperatures declined slightly from 1880 to 1910, then rose from 1910 to 1940, then declined from 1940 to 1970, then rose from 1970 to about 2000, and have declined slightly since.
So we are looking at a 130 year uptrend superimposed over a 60 year natural fluctuation. We can expect temperatures to be flat until around 2030, before starting another upleg into 2060.
Now obviously the 60 year cycle is natural. Now that it is obvious it is being explained in terms of PDO. The question is, does the longer 130 uptrend represent AGW, or another natural cycle with a longer period, or contributions from both?
The short answer is "we don't know - yet". The magnitude of the change is about right if a doubling of CO2 leads to a 1 degree temperature rise, and the positive and negative feedback cancels out.
But a change of that size could also be explained by natural variability - a cursory glance at the temperature record for the last 4000 or 4 million years should show that there is no real stability.
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