Hacker News Reader

Comment by alecst | Hacker News Reader

Can you elaborate on this part?

    * Science isn't clear regarding what part of global temperature rise is due to human activity.

I just want to contrast the above with this statement by the IPCC [1]:

"Human influence has been detected and attributed in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, and in global mean sea level rise; and has been extremely likely been the dominant cause of the observed warming since the mid century. In recent decades, changes in climate have caused impacts on natural and human systems on all continents and across the oceans."

[1] https://www.ipcc.ch/pdf/assessment-report/ar5/syr/drafts/SYR...

View on HN

>"[human activity] has been extremely likely been the dominant cause of the observed warming since the mid century."

This is worded strangely so that it doesn't mean anything. Of course human activity has been the dominant cause of humans observing something. Why don't they say CO2 emitted by human-made machines or something more specific?

That reply doesn't address my original comment, but the IPCC do say just that -- although not in that paragraph. You will find statements all over the IPCC about how climate change is nearly certain to be caused by people, and in particular, by people burning fossil fuels. If you go to the link I posted and search for "fossil" you will that in those notes. You can also read the official IPCC reports yourself to get a clearer idea.

Maybe I'm misunderstanding you, but there's no anthropic principle at work. It would be perfectly fine to say (although it would not be true) that "plasma fluctuations on the surface of the sun are extremely likely to be the dominant cause of observed warming since the mid century."

I was just commenting on the strange word choice used for that statement. Almost like whoever was editing that section wanted a way to weasel out of the implications later, if need be.

"climate change" isn't caused by people unless you think the climate never changed before humans were involved.

The question is what portion of the change is contributed by recent human industrial activity and I don't think that is particularly well quantified.

This page has a graph that shows how global temperature changes are part of cycle that has existed longer than humanity.

http://earthobservatory.nasa.gov/Features/GlobalWarming/page...

I was pointing out that the human induced part of the rise isn't quantified very well (large error bars, lots of handwaving), not that there is no human induced warning.

That's alright. I just want to know why you say that it's handwavey. As far as I knew there was almost no dispute that CO2 had huge and well-quantified warming potential. Nor was there a debate about the origin of the CO2 in the atmosphere (from the ratio of carbon-14/13 to carbon-12, you can tell it's from fossil fuels.) Please correct me if this is mistaken, because it's not my field of expertise.

The amount of CO2 in the atmosphere is well quantified and there are estimates regarding how much of this is caused by human activity that don't appear to be source of too much controversy. The warming caused by CO2 is relatively clear, and not seriously disputed.

But the direct warming due to CO2 is not what triggers all the public debate about climate change. That comes from the indirect warming associated with hypothesized positive feedback mechanism within the Earth's climate. There is no settled science on this indirect warming so the net affect of human-activity (the measured CO2 in the atmosphere contributed by human activity) is unclear. The climate models have historically over-estimated this net affect when their predictions are compared to the actual measurements.

Reply on news.ycombinator.com