Javier again on Judith Curry's site.
Probably the one "negative" effect that can be traced to an increase in man-made CO2: loss of ice in the cryosphere--glaciers and polar ice. Old trees along with human artifacts are being exposed by meling ice in various locations, and dating shows that they have been covered by ice for thousands of years. There is now a specialized field of study that focusses on newly exposed items in order to study them before they decay as they are exposed to the elements.
For some reason, Antarctica is the great exception: ice not in decline there, and temperature not increasing.
Does the loss of ice in many different areas of the globe support the view that CO2 on its own causes significant changes to climate? Not necessarily. The cryosphere combines cold temperatures with low humidity, meaning a low capacity to produce water vapour in a situation of warming, even non-dramatic warming, and these may be the pre-conditions that allow CO2 to have its effect. If so, H2O may show a negative feedback, limiting any warming, not a positive feedback, magnifying warming, as is indicated in the official IPCC literature. All of the surface of the globe that is not in the cryosphere may be different from the cryosphere, mainly because of high humidity, and CO2 may be much less effective there because of more water vapour. If H2O is more of a decisive factor than CO2 alone, this might explain why temperature has not gone up anywhere near in tandem with increasing CO2, and sea level rise has not changed significantly.
1) Modern Global Warming is one of several multi-centennial warming periods that have taken place in the last 3000 years.
2) Holocene climate cycles project that the period 1600-2100 AD should be a period of warming.
3) A consilience of evidence supports that Modern Global Warming is within Holocene variability.
4) Modern Global Warming displays an unusual non-cyclical cryosphere retreat. The contraction appears to have undone most of the Neoglacial advance.
5) The last quarter (70 yr) of Modern Global Warming is characterized by extremely unusual and fast rising, very high CO2 levels, higher than at any time during the Late Pleistocene. This increase in CO2 is human caused.
6) The increase in temperatures over the past 120 years shows no perceptible acceleration, and contrasts with the accelerating CO2 forcing.
7) Sea level has been increasing for the past 200 years, and its modest acceleration for over a century shows no perceptible response for the last decades to strongly accelerating anthropogenic forcing.
8) The evidence supports a higher sensitivity to increased CO2 in the cryosphere, which is driving unusual melting and a small long-term sea level rise acceleration. The rest of the planet shows a lower sensitivity, indicating a negative feedback by H2O, that prevents CO2 from having the same effect elsewhere.
Update Feb. 27: Judith Curry comments to the effect that soot may have an effect, independent of CO2 and water vapour, in causing ice loss in the northern hemisphere. Soot may be relatively easy to manage.
Update Mar. 4: Pierre Gosselin goes over a number of papers, including Allan et al 2018, on Arctic Sea Ice: not the same as "temperatures + ice in the northern hemisphere cryosphere."
Tremendous variation in the amount of sea ice in the Arctic throughout the holocene, in no way in sync with CO2 levels. Allan et al: West Greenland sea ice: from 1900 to 2007, both warmer surface conditions and reduced sea ice; but when you look closely at their graph, most of the lowest values were from the 1920s to the 1940s. This agrees with Kryk et al 2017, who say that in Southwest Greenland, overall sea ice concentration has grown dramatically since the 1930s.
Pierre Gosselin of No Tricks Zone: "my non-alarmist view is subject to change at any time."