Good news on Climate Change front

[caraher]

9. Here are a few from 2014

It's worth remembering that peer-reviewed literature is never the last word, with results that are mostly not obviously wrong. The current literature in any field of active research ought to contain some contradictions and disagreements. But since you asked for different views from the peer-reviewed literature, here are a few, followed by the end of a paper in preparation by an economist asking what the policy conclusion should be based on recent reassessments of climate sensitivity (hint: it's not using papers suggesting the low end of the range and concluding we need not take swift action)

A Nature abstract

Equilibrium climate sensitivity refers to the ultimate change in global mean temperature in response to a change in external forcing. Despite decades of research attempting to narrow uncertainties, equilibrium climate sensitivity estimates from climate models still span roughly 1.5 to 5 degrees Celsius for a doubling of atmospheric carbon dioxide concentration, precluding accurate projections of future climate. The spread arises largely from differences in the feedback from low clouds, for reasons not yet understood. Here we show that differences in the simulated strength of convective mixing between the lower and middle tropical troposphere explain about half of the variance in climate sensitivity estimated by 43 climate models. The apparent mechanism is that such mixing dehydrates the low-cloud layer at a rate that increases as the climate warms, and this rate of increase depends on the initial mixing strength, linking the mixing to cloud feedback. The mixing inferred from observations appears to be sufficiently strong to imply a climate sensitivity of more than 3 degrees for a doubling of carbon dioxide. This is significantly higher than the currently accepted lower bound of 1.5 degrees, thereby constraining model projections towards relatively severe future warming.

Despite important advances in other areas of climate science, we have discovered new uncertainties that make us even less confident about the range of equilibrium climate sensitivity than we were before the publication of the latest IPCC report. Given the increasing marginal costs of global warming, greater uncertainty, other factors equal, has an unambiguous implication for policy. It raises the return for taking action to curb greenhouse emissions.


Abstract of Nature: Climate Change paper concluding that the lowest end of sensitivity estimates is unlikely:

Understanding climate sensitivity is critical to projecting climate change in response to a given forcing scenario. Recent analyses1, 2, 3 have suggested that transient climate sensitivity is at the low end of the present model range taking into account the reduced warming rates during the past 10–15 years during which forcing has increased markedly4. In contrast, comparisons of modelled feedback processes with observations indicate that the most realistic models have higher sensitivities5, 6. Here I analyse results from recent climate modelling intercomparison projects to demonstrate that transient climate sensitivity to historical aerosols and ozone is substantially greater than the transient climate sensitivity to CO2. This enhanced sensitivity is primarily caused by more of the forcing being located at Northern Hemisphere middle to high latitudes where it triggers more rapid land responses and stronger feedbacks. I find that accounting for this enhancement largely reconciles the two sets of results, and I conclude that the lowest end of the range of transient climate response to CO2 in present models and assessments7 (<1.3 °C) is very unlikely.

Another abstract, this from Geophysical Research Letters. What's interesting here is that they assess how much data would be needed to really nail down climate sensitivity, and by this analysis we're 15 years' worth short of being able to make with confidence the distinction between the lower values in the papers touted in the OP and 3 degrees.

Equilibrium climate sensitivity measures the long-term response of surface temperature to changes in atmospheric CO2. The range of climate sensitivities in the Intergovernmental Panel on Climate Change Fifth Assessment Report is unchanged from that published almost 30 years earlier in the Charney Report. We conduct perfect model experiments using an energy balance model to study the rate at which uncertainties might be reduced by observation of global temperature and ocean heat uptake. We find that a climate sensitivity of 1.5°C can be statistically distinguished from 3°C by 2030, 3°C from 4.5°C by 2040, and 4.5°C from 6°C by 2065. Learning rates are slowest in the scenarios of greatest concern (high sensitivities), due to a longer ocean response time, which may have bearing on wait-and-see versus precautionary mitigation policies. Learning rates are optimistic in presuming the availability of whole ocean heat data but pessimistic by using simple aggregated metrics and model physics.

This is from a non yet peer-reviewed draft paper from an economist, but speaks to what we ought to conclude concerning policy from revised estimates. The conclusion:

Despite important advances in other areas of climate science, we have discovered new uncertainties that make us even less confident about the range of equilibrium climate sensitivity than we were before the publication of the latest IPCC report. Given the increasing marginal costs of global warming, greater uncertainty, other factors equal, has an unambiguous implication for policy. It raises the return for taking action to curb greenhouse emissions.