Steve E. Koonin, a theoretical physicist of some standing in the community, has an essay, in the Wall Street Journal on climate change aka Global Warming, entitled, Climate Science is not Settled. It could have been called Climate Science is not Settled nor is it a Hoax. Then it would be easier to understand why it will catch flak from both extremes of the climate change debate. If you are trying to figure out which factions are clueless in the debate, just look for Koonin bashers. In the essay Koonin lists three challenging fundamentals.
The first, Even though human influences could have serious consequences for the climate, they are physically small in relation to the climate system as a whole. For example, human additions to carbon dioxide in the atmosphere by the middle of the 21st century are expected to directly shift the atmosphere's natural greenhouse effect by only 1% to 2%. Since the climate system is highly variable on its own, that smallness sets a very high bar for confidently projecting the consequences of human influences.
If you consider that the "normal" greenhouse effect produces a lower atmospheric average temperature of about 4 C degrees, the impact of a "normal" GHE would be about 334 Wm-2. A 1% increase would be 3.4 Wm-2 and a 2% increase would be 6.8 Wm-2. That is roughly the range of impact based only on the CO2 portion of the anthropogenic changes to the atmosphere. If you are looking for impact in terms of temperature, then the "average" change in temperature would be 0.7 C for the 1% and 1.4 C for the 2% impacts. Since this is based only of the CO2 change, these would be "no feedback" estimates for the Greenhouse Effect.
A second challenge to "knowing" future climate is today's poor understanding of the oceans. The oceans, which change over decades and centuries, hold most of the climate's heat and strongly influence the atmosphere. Unfortunately, precise, comprehensive observations of the oceans are available only for the past few decades; the reliable record is still far too short to adequately understand how the oceans will change and how that will affect climate.
There is currently some controversy surrounding the lower than anticipated rise in "average" global surface temperatures. This hiatus, pause, slowdown or hiccup has been contributed to a variety of potential "causes", but the most recognized is a change in the rate of ocean heat uptake. Since the "average" energy of the global oceans would be related to the "average" temperature of the global oceans which is about 4 C degrees, no feedback on the global oceans should be about the same as the no feedback impact on the lower troposphere, i.e. global average Down Welling Longwave Radiation (DWLR) which is roughly estimated to be 334 Wm-2. Challenge one and two are likely linked.
A third fundamental challenge arises from feedbacks that can dramatically amplify or mute the climate's response to human and natural influences. One important feedback, which is thought to approximately double the direct heating effect of carbon dioxide, involves water vapor, clouds and temperature.
Atmospheric water vapor and clouds are directly related to the ocean and lower troposphere temperatures, absolute temperatures not anomalies, so water vapor and cloud "feedback" would be related to any cause of temperature change, not just changes "caused" by CO2. The third challenge is directly related to the first two challenges.
If you follow the "believers" of dangerous Anthropogenic Global Warming which has been repackage with terms like "climate change" or "climate disruption", they will most likely point out fallacies in Koonin's essay that are related to "beliefs" that all warming and all feedbacks are due to anthropogenic "causes". If you follow the "hoaxers", they will argue that the "physics" violates some law of thermodynamics or that there is no direct, indisputable measurement of CO2 impact.
Koonin's essay should equally piss both extremes off which is in my mind a great scientific and social evaluation of the issue. So anyone that vehemently disagrees with Koonin is likely a whack job or has a political ax to grind.
Those less agenda driven will notice that there are three "states" that would need to be in thermodynamic equilibrium for "standard" physics to easily apply, the ocean temperature would have to be in equilibrium with the lower atmospheric temperature while atmospheric water vapor and cloud conditions would have to be in equilibrium with both of the other two conditions.
If a body A, be in thermal equilibrium with two other bodies, B and C, then B and C are in thermal equilibrium with one another. Is a simple way to state the zeroth law of thermodynamic. That would be the only "law" of thermodynamics that might be violated in the climate change debate. What it boils down to is you have to know the "normal" condition of the atmosphere, oceans and cloud cover if you are going to determine impact of any change in any of the "initial" conditions. If you pick a variety of "initial" conditions and get a variety of answers that are inconsistent, then you didn't have the Zeroth Law equilibrium requirements met or your theory is wrong. The smaller the range of inconsistencies, the less wrong you are likely to be. The first estimate is the 1% to 2% "no feedback" or all other things remaining equal condition of 0.7 to 1.4 C degrees, is the one to beat.