Climate Known Unknowns 2 - ORIGINAL CONTENT

 “There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we know we don't know. But there are also unknown unknowns. There are things we don't know we don't know.”   Donald Rumsfeld

Climate sensitivity to atmospheric CO2 concentration is unknown.

The consensed climate science community’s focus on CO2 makes the Equilibrium Climate Sensitivity (ECS) of the climate to atmospheric CO2 concentration a critical focus of climate research. Historically, climate sensitivity estimates have been derived from climate model studies. More recently, scientists have been developing data-driven estimates of sensitivity, which tend to be lower than the estimates derived from model runs.

Taken by itself, ECS is slightly greater than 1. However, model derived ECS estimates range from 2.5 – 4.0 (IPCC AR6), while data derived estimates range from 1 - 2. The difference between the stand alone ECS estimate and the more widely reported values are the result of estimates of feedback effects, predominantly the anticipated increase in atmospheric water vapor content as the result of increased evaporation caused by warming. However, data suggest that there has been no measurable change in atmospheric water vapor content.

Climate forcings are uncertain.

The primary climate forcing is the short wavelength infrared radiation from the sun. Other forcings include the positive and negative effects of clouds, the long wavelength infrared radiation absorption by greenhouse gases, the short wavelength absorption by atmospheric aerosols and changes in the earth’s albedo. The effects of clouds are not well understood and are not treated by the climate models.

Climate feedback magnitude and sign are undetermined.

As mentioned above, the climate models include assumptions regarding positive feedback effects on ECS. However, these feedbacks are not measurable. Satellite studies suggest that the feedbacks are either non-existent or negative.

The eruption of the Hunga Tonga volcano increased the water vapor content of the troposphere and the stratosphere by an estimated 10-13% and increased atmospheric warming. However, in this case, the water vapor effect was a forcing and not a feedback.

Climate models predict different future conditions.

There are numerous climate models which produce varying results depending on the input conditions and assumptions. It is not certain that any of these models accurately models the real climate, or that the potential future of the earth’s climate falls within the range of model estimates. Therefore, since the models do not accurately reflect the function of the real climate, they are unsuited to predicting the climate future.

Future concentration pathways are unknown.

One of the key uncertainties in climate modeling is the future atmospheric CO2 concentration, which is a function of the selected Representative Concentration Pathway (RCP) selected as the model input. Future concentrations are unknown, but are estimated based on expected future fossil fuel use.

Climate change effects on weather are uncertain.

IPCC (AR6) assigns low confidence regarding any effects of climate change on weather events, now or through the end of the century. Attribution studies assert that climate change has identifiable impacts on the frequency and/or intensity of weather events. However, these assertions are based on unproven climate models and are unverifiable.

Climate change effects on agriculture are uncertain.

Increased atmospheric CO2 concentrations have been identified as contributing approximately 70% to the observed global greening, both because of atmospheric fertilization and improvements in the efficiency with which plants use available water. Increased atmospheric CO2 also contributes to the growth rates of most food crops, contributing to continuing record harvests.

Rate of sea level rise uncertain.

There remain significant differences between the rates of sea level rise measure by tide gauges and those measured by satellites. The tide gauges measure a steady and modest rate of rise. The satellites measure a rate of rise nearly double the rate measured by the tide gauges; and, the satellites supposedly detect an increase in the rate of rise.

The known unknowns represent significant opportunities for “Gold Standard” climate research.

Unknown unknowns represent a potential future challenge of unknown proportions.