Nansen Center scientist contributes to IPCC 5th Assessment Report: The observational evidence basis

The Intergovernmental panel on Climate Change (IPCC) has released today the Working Group 1 contribution to their Fifth Assessment Report in Stockholm. Nansen Center Senior Scientist Peter Thorne’s has through his publications and scientific capacity contributed as a Lead Author to the IPCC WG1 report. Dr. Thorne has contributed to the final revisions of the report during the last week and is attending the plenary release in Stockholm today [1]. As well as being a Lead Author on Chapter 2, Dr. Thorne is a contributing author to the Summary for Policy Makers, Technical Summary and Chapters 9 and 10 of the main report.

Below follows some of the key research issues in which Dr. Thorne has been involved.



[1] Peter Thorne was nominated by the UK government and accepted as a Lead Author on Chapter 2 – atmospheric and surface observations; undertook most of the work whilst in the United States; and is now Senior Scientist at the at the GC Rieber Climate Institute at the Nansen Center.

 

Figure showing multiple indicators of a world that has warmed. Each trace represents a different data product from a different research group: Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Figure showing multiple indicators of a world that has warmed. Each trace represents a different data product from a different research group: Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.The observational evidence for our changing climate is wide ranging. From high in the atmosphere to deep in the oceans a broad range of indicators are consistent in pointing to a world that has warmed since the late 19th Century. Those indicators we would expect to increase in a warming world such as land and ocean surface temperatures, atmospheric temperatures, ocean heat content, sea level and atmospheric specific humidity have all increased. At the same time spring snow cover, arctic sea ice, and global glacial mass have all decreased as we would expect to happen in a warming world. Multiple estimates from multiple groups, including scientists at the Nansen Center, confirm this for each and every indicator. It is unequivocal that the world has warmed since the late 19th Century.

 

 

 

 

 

 

 

 

 

Decadal mean anomalies in Global Mean Surface Temperatures and their recognized, quantified uncertainties in HadCRUT4: Figure arises from Met Office Hadley Centre, and from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Decadal mean anomalies in Global Mean Surface Temperatures and their recognized, quantified uncertainties in HadCRUT4: Figure arises from Met Office Hadley Centre, and from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Global Mean Surface Temperature has increased since the late 19th century.  Each of the past three decades has been significantly warmer than all the previous decades in the instrumental record based upon recognized quantified uncertainties, and the first decade of the 21st century has been the warmest.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Trends in surface temperature across the globe: Trends are ordinary least squares regression fits where enough data exist. Trends which are significant are highlighted by crosses. Significance testing accounts for autocorrelation effects (that one year being warm increases chances of following year being warm and vice-versa). Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Trends in surface temperature across the globe: Trends are ordinary least squares regression fits where enough data exist. Trends which are significant are highlighted by crosses. Significance testing accounts for autocorrelation effects (that one year being warm increases chances of following year being warm and vice-versa). Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.The global combined surface temperature data show an increase of about 0.85°C (0.65°C–1.06°C) over the period 1901– 2012 when described by a linear trend. Warming has occurred across almost the entire globe.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Timeseries of annual mean global mean surface temperature anomaly estimates: Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Timeseries of annual mean global mean surface temperature anomaly estimates: Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.

The rate of warming over 1998–2012 (0.05°C [–0.05 to +0.15] per decade) is smaller than the trend since 1951 (0.12°C [0.08 to 0.14] per decade). Various mechanisms including natural variability, volcanic and solar influences, and possible model biases have been invoked to explain this reduced warming rate and why it is not seen in most of the climate model simulations.  Some combination of these is likely to explain this issue.

 

 

 

 

 

 

 

 

 

 

Atmospheric temperature trend estimates since 1979 when routine satellite monitoring began: The troposphere (up to around 300hPa at the poles and 150hPa in the tropics) is warming and the stratosphere cooling. The upper panels show satellite deep layer estimates for LT (‘lower troposphere’), MT (‘mid troposphere’) and LS (‘lower stratosphere’). Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Atmospheric temperature trend estimates since 1979 when routine satellite monitoring began: The troposphere (up to around 300hPa at the poles and 150hPa in the tropics) is warming and the stratosphere cooling. The upper panels show satellite deep layer estimates for LT (‘lower troposphere’), MT (‘mid troposphere’) and LS (‘lower stratosphere’). Figure arises from IPCC WGI AR5 Final Draft 07 June and is subject to potential copy editing and change prior to final publication per documentation to be released after final plenary.Changes in diurnal temperature range over land (the difference between daytime maxima and nighttime minima) are still relatively poorly known. Some studies have indicated a partial reversal of a decreasing diurnal temperature range in recent decades while others have highlighted potential significant unresolved data issues. Here, the work of Nansen Center colleagues and international collaborators may help both in developing our understanding of the observational record and its causes / interpretation over coming years.

On a global scale unaccounted for urban heat island impacts (the fact that cities tend to be warmer than their surroundings) are unlikely to account for more than 10% of the multidecadal observed warming. Locally and regionally the effect may be greater.

The troposphere (lower 12 Km or so where the weather occurs) has warmed and the stratosphere (above) has cooled since the mid-20th Century. Given the increased number of estimates and improved understanding of the datasets and their ranges over recent years there is low confidence in the details of the vertical temperature trend structure away from the well sampled Northern Hemisphere mid-latitudes.

 

 

 

 

 

Scientists at the GC Rieber Climate Institute at the Nansen Center will continue to strive to contribute to our understanding of observed climate change and its causes to provide timely and critical inputs to the public, government, industry and future assessment activities.

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