Climate Change

[Alan V]

First of all, trends in the Northern Hemisphere are not necessarily world trends.

You have an example of one hemisphere going the other way to the other over a 180 year period? Or for that matter any multidecadal period?

I mean  that's kind of nuts to claim each hemisphere was doing something different, you know that right?

Yes, that was my mistake. It was too early in the morning and I was thinking in terms of local variations, which are of much shorter duration.

Second, "The planet's average surface temperature has risen about 1.62 degrees Fahrenheit

You lost all credibility when you quote Fahrenheit.

Here is the complete original quote: Second, "The planet's average surface temperature has risen about 1.62 degrees Fahrenheit (0.9 degrees Celsius) since the late 19th century, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. Most of the warming occurred in the past 35 years, with the five warmest years on record taking place since 2010." In other words, scientists know the present changes in temperatures are caused by greenhouse gas emissions. This is per: https://climate.nasa.gov/evidence/

Please note that it included Celsius as well as Fahrenheit, so it confirmed your assertion that total recent warming has been less than 1C. I assume your truncating the quote was a mistake on your part, since you thought I was trying to pull a fast one about total warming. But the quote was used to emphasize that we know present warming is caused by greenhouse gases, as was indicated by the original bolding.

Third, and I can't emphasize this enough: Scientists know the climate varied in other periods, and typically also know what caused those variations.  They were not caused by human emissions of greenhouse gases.

Okay, so what precisely caused the warming trend in the reference years I gave - 804-990?

To be clear - the trend is nearly identical to what we're experiencing now, yes? And I could have cherrypicked an even shorter ranger that shows a steeper rise in temperature compared to say the last 40 years.

You mean you don't know what caused the warming trend between 804 and 990? What kind of climate scientists are you? Oh yeah, none at all.

You keep talking as if scientists, and even the general public, are unaware the climate has always shown both long-term changes and temporary variations.  You are incorrect.  You also keep talking as if we don't know for a fact that present changes are caused by emissions of greenhouse gases.  This is untrue.

And now you're straw-manning. That should be given a new meaning - I henceforth declare we call it strawManning.

We don't know "for a fact" anything of the sort. If you bother to read the IPCC report (or the "consensus") it says they have 95% confidence to say that anthropogenic GHGs are contributing something greater than 50% of the total trend. There's a 1 in 20 chance, according to their own statistical maths, that they're wrong.

First of all, I have read a range of books from a number of climate scientists, not just Michael Mann, most all of which refer back to IPCC reports, which summarize peer-reviewed worldwide climate science studies. So this can be dismissed as a cheap shot.

Second, here is the reference I mentioned above:

https://www.reuters.com/article/us-clima...SKCN1QE1ZU

Evidence for man-made global warming has reached a “gold standard” level of certainty, adding pressure for cuts in greenhouse gases to limit rising temperatures, scientists said on Monday.

“Humanity cannot afford to ignore such clear signals,” the U.S.-led team wrote in the journal Nature Climate Change of satellite measurements of rising temperatures over the past 40 years.

They said confidence that human activities were raising the heat at the Earth’s surface had reached a “five-sigma” level, a statistical gauge meaning there is only a one-in-a-million chance that the signal would appear if there was no warming.

...

Peter Stott of the British Met Office, who was among the scientists drawing that conclusion and was not involved in Monday’s study, said he would favor raising the probability one notch to “virtually certain”, or 99-100 percent.