Tidal estimates from sediment cores go even further back to the 1300's. They find sea level rise is close to zero in the early part of the sedimentary record. They then observe an acceleration in sea-level rise during the 19th and early 20th century. Over the period where the two datasets overlap, there is good agreement between sedimentary records and tidal gauge data (Donnelly 2004, Gehrels 2006). What we're most interested in is the long term trends. Figure 2 shows 20 year trends from the tidal data. From 1880 to the early 1900's, sea level was rising at around 1mm per year. Throughout most of the 20th century, sea levels have been rising at around 2mm per year. In the latter 20th century, it's reached 3mm per year. The five most recent 20-year trends also happen to be the highest values. https://www.skepticalscience.com/sea-level-rise-intermediate.htm
The Earth would cool while the atmosphere near the Earth would warm some. But that is a gross over simplification. What I have been attempting to convey is that the extent of warming of the lower atmosphere might be quite negligible, depending on the concentration and distribution of green house gas, and of course its absorption characteristics. It is not enough to say this or that gas is a greenhouse gas. Also, It would not be possible to eliminate the cooling contribution of vertical convection driven by density difference between the surface and the upper atmosphere. When you have, for example, other much more important temperature moderating components of the atmosphere, the contribution of such a weak greenhouse gas as CO2, at a very small concentration, may be negligible. My best guess, it is only that, is that we need CO2 to maintain plant life, without which all animal life would parish, but it is an incidental and unimportant direct contributor to global temperature moderation. I could be wrong but our best and most recent data suggests to me that my guess is probably close to the actual situation. I think you may have missed my main point which was that if Hansen's hypothesis depends on there being positive feedback to the effect of elevating CO2 than Hansen's hypothesis is wrong. And importantly everything dependent on Hansen's hypothesis being right is therefore also wrong. Would you at least agree with that?
Speaking only to Hansen's hypothesis... I don't care. We don't need a positive feedback loop if we're going to continue adding CO2 anyway.
But there is no question that positive feedbacks are happening. The albedo of the Arctic has decreased and methane and CO2 contained in permafrost is being released as temps rise. But you are right about one thing, CO2 is used by plants. Huge festering pile.
To achieve the dangerous exponential rise in temperature that Hansen hypothesized, positive feedback is needed. This is a feature of all the models predicting exponential rise. It would be very difficult add CO2 at a rate that would exceed the ecosystems ability to absorb it and convert it to bicarbonate, carbonate, and carbohydrates . However if we destroy the Earth's flora by clearing enough land and increase our pollution of the oceans we might achieve this . Ever increasing human population might do it in a few millenia . I think we should at least consider warming by direct thermal pollution. We already can observe that in the Urban Island Effect.
These cartoons come amazingly close to a succinct summing up of the current situation. The last box however, rather than being blank or black, could be a large question mark. We have learned a lot about climate since Hansen and his GISS colleagues began raising questions regarding the possibility that man's accelerated production of CO2 might be affecting our global average temperature. Yet despite all our progress, we still don't know the answer because the problem has turned out to be far more difficult than those who jumped to premature conclusions might have guessed. At this point we have new unanswered questions that have to answered before we can go forward in the scientific sense. A major question that remains unanswered is why is the satellite temperature data in disagreement with the surface monitored data? The surface readings indicate the Earth is warming, and incidental direct observations, such as melting of the polar ice caps, are consistent. The Satellite data, however, indicates negligible warming overall within experimental error. This is a BIG problem. Until it's resolved we can't rely on either the ground or the satellite observation. We will likely move ahead in the social sense before we have the answers. This is a mistake! If we act on a questionable hypothesis, we will muddy the waters and make the resolution of that hypothesis even more difficult. The mistake might be justified if our working hypothesis was still intact. But there are observations that are inconsistent with the hypothesis. And an hypothesis, which is an educated guess, can't be accepted as scientifically correct until all descrepancies between observation and the hypothesis are resolved. This is no way to do science. But then we aren't doing science . We are doing politics. Pity.