Thanks for getting permission, Tiruin. Here's some commentary/nitpicking, then:
#3 I actually didn't have any problems with - the word
primary works in this case, as there are indeed other factors that change the climate (both in the 'warming' and 'cooling' directions) but over the time period of the phenomenon it's majority - or primarily - anthropogenic.
Same with #2 - the '98% of scientists' figure is actually kind of bogus (that particular study was only a limited cross-section of the profession), but the vast majority of scientists still do agree. There are some scientific fields with higher rates of dissent, but if I recall correctly the majority even in those fields believe the evidence supports the theory of climate change / global warming.
The use of the word 'global warming', while it polls better to the public, is less accurate than 'climate change'. Due to the various ways that climate change affects the existing order, increased GHGs can actually lead to colder, more intense winters for certain parts of the world (in certain periods of time). Other changes, such as more intense rains, aren't really 'warming' or 'cooling' but changes in other variables of the climate as the levels of carbon dioxide and greenhouse gases increase. And then there's ocean acidification, which is kind of a parallel event but I'd argue can be considered part of climate change.
For #5, answer B strikes me as at least partially a subset of A. Got a bit to say on this question generally, but I'll say at the outset that I'm assuming "sources of energy" is referring to the power sector. If not, the below still applies but not quite as strongly. I'll spoiler the further discussion to spare folks' eyes.
Reducing existing emissions includes reducing emissions in the power sector; developing and deploying cleaner sources of power will, if you're actually replacing the old plants, reduce existing emissions. While true that in many developing nations there's more 'future power' than 'existing power' (as Tiruin rightly points out), cleaner energy isn't the end-all-be-all solution to the world's emission problem. Just as other countries are increasing their power sector output, they're also increasing the number of personal & commercial vehicles, refrigerant usage, etc.
Further for #5 answer B, developing cleaner sources of energy does not necessarily help across all sectors. In the U.S. these days the percentage of carbon-equivalents from the power sector has been going down to the mid-30s%; even if we suddenly eliminated all power-sector emissions in the U.S., we'd still be emitting a lot of greenhouse gases. At this point may be overtaken by emissions from the transportation sector within a few years. Unless we develop and deploy both new transportation fuels (e.g. electricity or hydrogen fuel cells) and the infrastructure to support them (e.g. charging stations instead of gas stations), a new energy source won't help much. There's a big difference between developing utility-scale energy and 'household device'-scale energy.
Other examples include the concept of 'electrification' - if everybody is still heating their homes with natural gas, then having cleaner power reactors doesn't help reduce emissions from home heating. Agricultural sources are significant (if smaller) and energy sources won't do anything about that. Industrial processes emit a fair amount of GHGs, too, and in many cases cleaner energy sources won't address those processes. Finally, energy efficiency! Making our appliances, tools, vehicles, etc. etc. all more energy efficient has - and likely will be - an enormous driver of reduced emissions; the energy we don't have to produce is a lot cheaper than the fancy new clean energy source we can construct. Energy efficiency isn't free, of course, as developing the improved efficiency and the cost of producing the more efficient product aren't zero, but thus far it's got a good track record.
For another example, the Montreal protocol (the 'ozone hole' treaty) was recently updated to address the fact that one of the refrigerant chemicals that replaced the ozone-hole-causing chemicals is actually a 'super greenhouse gas'. If the new amendment to the treaty is properly implemented, the world is expected to avoid a full 0.5 degrees (C) of warming that would have occurred under a 'business as usual' scenario.
[This all generally ignores cost-effectiveness, too - while it's certainly important to develop things like fusion power, the same amount of resources required for a 'crash program' instead applied to other reductions strategies could arguably lead to greater net reductions, given the types of other clean energy technologies that are already making good progress and would just be supplanted by something like fusion power.]
Bottom line, from the research and modeling that I've seen there is no single silver bullet for reducing the effects of climate change. Suddenly having cheap fusion power tomorrow morning that could be easily integrated into the existing power grid (and have sufficiently low safety risks to reduce NIMBYism and difficulties in deploying in countries with civil societies able to resist such things whether rightly or wrongly) would be a pretty darn big deal, but not even get rid of the majority of U.S. emissions - in a scenario where, to get at something like 1.5 C, the world needs to have
negative emissions in the last few decades of this century.
Edit, in spoiler, in regards/response to Max™'s comments:
I empathize and agree with your criticisms, but would argue that speaking in terms of 'X degrees C' is a necessary abstraction in order to converse with policymakers, who are largely non-scientists, about the issues in a way that they can understand and hopefully act on.
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Topic: Discuss my completed survey! (100% of climate scientists acquired) (Read 5658 times)