Comments On The Second Web Posting By Kevin Trenberth on “Climate Feedback – The Climate Change Blog”

Kevin Trenberth has followed up his weblog on the Nature site Climate Feedback – The Climate Change Blog entitled “Predictions of climate” with a weblog on the subject of climate prediction. This new posting is entitled

Global Warming and Forecasts of Climate Change.

Unfortunately, this new post lacks the candor that is in the original Nature weblog by Kevin Trenberth on this subject (as discussed on Climate Science ; see).

The current weblog makes several misleading statements with respect to the ability to “project” climate change with the multi-decadal global climate models.

First, Trenberth writes,

“In particular there is clear evidence (“warming is unequivocalâ€?) that climate is changing in ways consistent with the climate forcings. Also, the projections are for all aspects of climate, not just global mean temperature.”

This obviously contradicts his statement in his first Nature weblog where he writes

“However, the science is not done because we do not have reliable or regional predictions of climate.”

The model results cannot be “consistent” if they are not reliable and are also not regional in scale!

Second, he writes,

“The same atmospheric models are the atmospheric component of climate models and they are well tested and evaluated, although in climate models lower resolution is used.”

This is true (except the weather models typically do not include atmospheric gaseous and aerosol chemistry which is required in a multi-decadal global climate model). However, as he writes in his first weblog,

“None of the models used by IPCC are initialized to the observed state and none of the climate states in the models correspond even remotely to the current observed climate. In particular, the state of the oceans, sea ice, and soil moisture has no relationship to the observed state at any recent time in any of the IPCC models. There is neither an El Niño sequence nor any Pacific Decadal Oscillation that replicates the recent past; yet these are critical modes of variability that affect Pacific rim countries and beyond. The Atlantic Multidecadal Oscillation, that may depend on the thermohaline circulation and thus ocean currents in the Atlantic, is not set up to match today’s state, but it is a critical component of the Atlantic hurricanes and it undoubtedly affects forecasts for the next decade from Brazil to Europe. Moreover, the starting climate state in several of the models may depart significantly from the real climate owing to model errors. I postulate that regional climate change is impossible to deal with properly unless the models are initialized.”

His own words present a very different perspective than given on his new weblog. The atmospheric models may be the same, but the other components of the climate model (ocean, land, cryosphere) are poorly represented!

Third, he writes,

“The authors should recognize that IPCC does not make forecasts but rather makes projections to guide policy and decision makers.”

This is disingenuous to suggest to readers that a forecast and a projection are any different; see

Pielke Sr., R.A., 2002: Overlooked issues in the U.S. National Climate and IPCC assessments. Climatic Change, 52, 1-11

He continues by seeking to separate a forecast from a projection because with a projection

“If those changes are considered undesirable, it can create efforts to change that outcome.”

This is obviously true of forecasts too (weather modification, for example, could change a forecast for rain, but the term projection is never used in this context). The term “projectionâ€? is only introduced, rather than forecasts, to obscure that the multi-decadal global models do not have predictive skill!

It should be clear in his new Nature weblog that, unfortunately, his candid comments in this earlier weblog resulted in negative feedback from his colleagues such that he felt compelled to follow up with a poor summary of climate forecasting. This is unfortunate, as his original weblog was a bridge that can be used to advance climate science.

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Filed under Climate Models, Climate Science Reporting

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