They disagree in exactly the way gjm mentions below.
Experts are climate scientists and scientists in related fields. Some politicians may be included as ‘experts’ in terms of solutions, too, I suppose. They disagree about the severity, cause, timeline and solution. And not by some trivial amount, but by enough to drastically shift priorities.
Also, while this is a reply to Eliezer’s 2007 comment, I’m aware the situation has changed. I really just want to know how to begin to form a rational belief about climate change as of now.
I find climate change a strange issue. Not the situation itself but the public response and political tactics that are used.
On the surface, it looks like the vaccination controversies where one side goes “you guys are stupid for completely ignoring science”. The difference is, the science for vaccines is rock solid. There is a negligible chance of vaccines hurting you. And we have an extremely large amount of evidence. Not evidence from computer models or something theoretical, but actual data from millions of people being vaccinated.
Climate change, no matter your opinion, cannot be said to be this sure of a thing. Yet the tactics used are the same. “If you don’t take up our cause, you are the enemy of Science.” Science isn’t some deity. I don’t obey out of some appeal to authority. It’s useful because it can convince me with reason.
If the issue is trivial or unanimous, I may just accept the scientific consensus at face value. But for a possible existential threat that could either kill us or cost an unimaginable amount of money to prevent… And there are experts that disagree! And the consensus has changed several times in the last few decades! And politicians are pushing a certain direction! …I’m not being ideological here, am I? This isn’t a black and white issue is it?
There are some black and white issues, where a valid comparison to antivax strongly holds, and some fuzzier issues where it holds weakly or not at all.
The strongest claim is that global warming is real and anthropogenic. This is very solid science, indeed pretty basic atmospheric physics. Nonetheless there are people in positions of power who argue that it is false. To make that argument is indeed to set oneself up in opposition to science—that is, opposed to the scientific method as a way to discover truth.
Denial of this basic truth is a serious enough problem that 18 scientific associations felt the need to issue a joint statement to that effect, backing up a further 200 with the same view.
The second strongest claim is that global warming is a threat to humanity, and that immediate action to reduce CO2 emissions to net zero (primarily through the use of fossil fuels) is essential to preserve human life.
This view is held and strongly advocated by every scientific association with any claim to relevant knowledge that I can find. For example the AAAS says that “global climate change caused by human activities is now underway, and it is a growing threat to society” and “The time to control greenhouse gas emissions is now” (when “now” was 2006). The AGU says that “Human activities are changing Earth’s climate, causing increasingly disruptive societal and ecological impacts” and “global carbon dioxide (CO2) emissions must reach net-zero by around 2070 to have a good chance of limiting warming to a 2° C increase and by about 2050 to achieve a more protective limit of a 1.5°C (2.7°F) increase”.In the last few decades, the consensus on the first issue has changed not at all; and on the second issue the only change has been a steady increase in the number of scientific associations willing to openly advocate immediate action.
To argue against action on climate change isn’t quite the same as arguing that vaccines don’t work, or that the germ theory of disease is false. It’s more like arguing that the cost of vaccines make them unjustifiable, or that surgeons generally have clean hands so scrubs and gloves are an unnecessary impost.
That’s about it though. After this you get to questions of *how* to decarbonise. There is far less consensus on that, and the issues are not so clear-cut. This gives plenty of wiggle room for anyone who would prefer not to decarbonise at all, by pushing the responsibility onto someone else, sending things to committee for debate, setting up processes that require full consensus between inimical participants before any action is taken, and so on.