Unforced Variations vs Forced Responses?

                          Guest commentary by Karsten Haustein, U. Oxford, and Peter Jacobs (George Mason University).

                          One of the perennial issues in climate research is how big a role internal climate variability plays on decadal to longer timescales. A large role would increase the uncertainty on the attribution of recent trends to human causes, while a small role would tighten that attribution. There have been a number of attempts to quantify this over the years, and we have just published a new study (Haustein et al, 2019) in the Journal of Climate addressing this question.

                          Using a simplified climate model, we find that we can reproduce temperature observations since 1850 and proxy-data since 1500 with high accuracy. Our results suggest that multidecadal ocean oscillations are only a minor contributing factor in the global mean surface temperature evolution (GMST) over that time. The basic results were covered in excellent articles in CarbonBrief and Science Magazine, but this post will try and go a little deeper into what we found.

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                          References

                          1. K. Haustein, F.E. Otto, V. Venema, P. Jacobs, K. Cowtan, Z. Hausfather, R.G. Way, B. White, A. Subramanian, and A.P. Schurer, "A limited role for unforced internal variability in 20th century warming.", Journal of Climate, 2019. http://dx.doi.org/10.1175/JCLI-D-18-0555.1

                          Unforced Variations: June 2019

                          Filed under: — group @ 3 June 2019

                          This month’s open thread for climate science discussions. Remember discussion about climate solutions can be found here.

                          Forced responses: May 2019

                          Filed under: — group @ 2 May 2019

                          A bimonthly open thread on climate solutions and policies. If you want to discuss climate science, please use the Unforced Variations thread instead.

                          Unforced variations: May 2019

                          Filed under: — group @ 2 May 2019

                          This month’s open thread about climate science topics. For discussions about solutions and policy, please use the Forced Responses open thread.

                          Nenana Ice Classic 2019

                          Filed under: — gavin @ 14 April 2019

                          Wow.

                          Perhaps unsurprisingly given the exceptional (relative) warmth in Alaska last month and in February, the record for the Nenana Ice Classic was shattered this year.

                          The previous official record was associated with the exceptional conditions in El Ni?o-affected winter of 1939-1940, when the ice went out on April 20th 1940. Though since 1940 was a leap year, that was actually a little later (relative to the vernal equinox) than the ice out date in 1998 (which wasn’t a leap year).?

                          Other records are also tumbling in the region, for instance the ice out data at Bethel, Alaska:

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                          While the trend at Nenana since 1908 has been towards earlier ice-out dates (by about 7 days a century on average), the interannual variability is high. This is consistent with the winter warming in this region over that period of about 2.5oC.? Recent winters have got close (2012/14/15/16) (3 to 4 days past the record),? but this year’s April 14th date is an impressive jump (and with no leap year to help calendrically).

                          As usual, I plot both the raw date data and the version adjusted to relative to the vernal equinox (the official time of breakup was ~12:21am).

                          ? [As usual, I predict that there will be no interest from the our favorite contrarians in this]

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                          ?First successful model simulation of the past 3 million years of climate change

                          Filed under: — stefan @ 3 April 2019

                          Guest post by Matteo Willeit, Potsdam Institute for Climate Impact Research

                          A new study published in Science Advances shows that the main features of natural climate variability over the last 3 million years can be reproduced with an efficient model of the Earth system.

                          The Quaternary is the most recent geological Period, covering the past ~2.6 million years. It is defined by the presence of glacial-interglacial cycles associated with the cyclic growth and decay of continental ice sheets in the Northern Hemisphere. Climate variations during the Quaternary are best seen in oxygen isotopes measured in deep-sea sediment cores, which represent variations in global ice volume and ocean temperature. These data show clearly that there has been a general trend towards larger ice sheets and cooler temperatures over the last 3 million years, accompanied by an increase in the amplitude of glacial-interglacial variations and a transition from mostly symmetry cycles with a periodicity of 40,000 years to strongly asymmetric 100,000-year cycles at around 1 million years ago.  However, the ultimate causes of these transitions in glacial cycle dynamics remain debated.

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                          Unforced variations: April 2019

                          Filed under: — group @ 2 April 2019

                          This month’s open thread on climate science issues. Remember that discussions about climate solutions go here.

                          Alpine glaciers: Another decade of loss

                          Filed under: — group @ 25 March 2019

                          Guest Commentary by Mauri Pelto (Nichols College)

                          Preliminary data reported from the reference glaciers of the World Glacier Monitoring Service (WGMS) in 2018 from Argentina, Austria, China, France, Italy, Kazakhstan, Kyrgyzstan, Nepal, Norway, Russia, Sweden, Switzerland and United States indicate that 2018 will be the 30th consecutive year of significant negative annual balance (> -200mm); with a mean balance of -1247 mm for the 25 reporting reference glaciers, with only one glacier reporting a positive mass balance (WGMS, 2018).

                          A view of how alpine glaciers in the Pacific Northwest fit into the broader ecosystem (Megan Pelto, Jill Pelto).
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                          References

                          The Crank Shaft

                          Filed under: — group @ 11 March 2019

                          This is a thread for collecting the oddball theories, tinfoil hat level conspiracies and other climate-related nonsense in the comments that would otherwise derail substantive discussion. Keeping them all in one spot might be of interest to future researchers.

                          Unforced variations: Mar 2019

                          Filed under: — group @ 3 March 2019

                          This month’s open thread on climate science topics.