Observed Climate Changes: An overview of recent assessments

The presenter has been a Lead Author in both IPCC and NCA activities and attended the Stockholm plenary of AR5. This talk will summarize the principal observational findings encapsulated within the fifth assessment report of the IPCC and the US National Climate Assessment. Particular emphasis will be given to changes in temperature and various aspects of the hydrological cycle, but other elements and domains will be touched upon.

Challenges associated with robustly assessing the rich ecosystem of observational estimates, and in particular their uncertainty estimates of greatly varying maturity and completeness will be outlined. This assessment of uncertainty estimates, and how to use these in subsequent evaluation of models is perhaps the biggest challenge facing a rigorous assessment of the observational evidence basis.

The talk will conclude with some reflections on the state of our knowledge of observed climate change and provide some thoughts on how we can strengthen the observational basis so that future assessment activities can take advantage of more robustly quantified observational estimates and associated uncertainty estimates. These include deploying and maintaining reference quality measurement networks, enabling meaningful intercomparisons between products for the same variable, and rescuing the unknown knowns – the large volume of pre-digital era data that languishes in numerous places.