Climate Known Knowns

We know more "what" than "why".

“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

Global near-surface land temperatures have increased.

The average increase is estimated to be approximately 1.6°C (2.9°F) by the agencies which maintain the records. The increase is not known precisely because many geographic areas do not measure temperature and many temperature measuring stations are affected by surrounding urban growth which increases temperatures.

Global tropospheric temperatures have increased.

The average increase is estimated to be approximately 0.95°C (1.7°F) since 1979, the beginning of the satellite record.

Global ocean temperatures have increased.

The global ocean surface temperature has increased approximately 0.9°C (1.6°F) over the past century. The bulk ocean temperature is not measured globally.

Atmospheric CO2 concentrations have increased.

Atmospheric CO2 concentrations have increased from a pre-industrial level of 270 ppm to 429 ppm, as measured at the Mauna Loa Observatory.

Atmospheric CO2 concentrations continue to increase.

Economic growth in developing nations, largely powered by fossil fuels, is causing annual anthropogenic CO2 emissions to continue to increase, despite global efforts to reduce emissions.

Increased atmospheric CO2 increases plant growth in numerous food crops.

Increases range from 10-15% in C4 crops to 33-40% in C3 crops. Most crops also use available water more efficiently under elevated CO2 conditions.

Global greening is occurring.

Observations from NASA satellites indicate that from one quarter to one half of earth’s vegetated area has greened over the satellite era and estimates that approximately 70% of the greening is the result of increased atmospheric CO2.

Global sea levels have risen.

Global sea levels have been rising since the trough of the Little Ice Age. Tide gauges estimate sea level rise approximately half the rise estimated by satellite measurements Satellite measurements suggest that the rate of sea level rise is increasing, though that is not the case of the tide gauges.

We know that we know these things based on instrumented observations. However, limited instrument coverage, short instrumental observation times, instrument site contamination and instrumental measurement differences limit the certainty of specific measurements.

Temperature anomaly measurements and sea level rise measurements are frequently reported to two decimal place precision. However, this level of precision is not justified based on the quality of the instrumentation sites and the differences between measurements made by different instruments.

Clearly, we have learned much about the changes in the earth’s climate over the period we have been recording instrumental measurements. We know, in general terms, what is happening, our “known knowns”. However, we have much to learn about why it is happening and how it will proceed in the future, our “known unknowns".

The are also likely some “unknown unknowns” which could have a major impact on our long-term future, possibly producing a “Black Swan” event.

Climate science is certainly not settled.

Originally published here.