A guest post by Nicholas Lewis
As many readers will be aware, I attended the WCRP Grand Challenge Workshop: Earth’s Climate Sensitivities at Schloss Ringberg in late March. Ringberg 2015 was a very interesting event, attended by many of the best known scientists involved in this field and in areas of research closely related to it – such as the behaviour of clouds, aerosols and heat in the ocean. Many talks were given at Ringberg 2015; presentation slides are available here. It is often difficult to follow presentations just from the slides, so I thought it was worth posting an annotated version of the slides relating to my own talk, “Pitfalls in climate sensitivity estimation”. To make it more digestible and focus discussion, I am splitting my presentation into three parts. I’ve omitted the title slide and reinstated some slides that I cut out of my talk due to the 15 minute time constraint.
In this part I will cover the first bullet point and one of the major problems that cause bias in climate sensitivity estimates. In the second part I will deal with one or two other major problems and summarize the current position regarding observationally-based climate sensitivity estimation. In the final part I will deal with the third bullet point.
In a nutshell, I will argue that:
- Climate sensitivity is most reliably estimated from observed warming over the last ~150 years
- Most of the sensitivity estimates cited in the latest IPCC report had identifiable, severe problems
- Estimates from observational studies that are little affected by such problems indicate that climate sensitivity is substantially lower than in most global climate models
- Claims that the differences are due to substantial downwards bias in estimates from these observational studies have little support in observations.