New Paper on Alaska Climate Trends

Filling a gap in the peer-reviewed literature

Alaska and most of the rest of the Arctic are warming much faster than the low and mid-latitudes. While Brian Brettschneider, myself and few other folks spend a lot of time working on Alaska and Arctic climate trends, often producing and distributing analyses in near-real time for use in various contexts, peer-reviewed publications are an essential part of the western science process. With the rapid pace of change at high latitudes, increasing in-situ data limitations and advances in climate science, the time was right for a rigorous update.

The impetus for this paper was the forthcoming Fifth National Climate Assessment, which has strict criteria regarding literature that can be cited. So during the winter of 2021-22 several of us got together and decided to work up a paper that would be a significant contribution to understanding the changes to the climate system in Alaska and around Alaska. The end result of that process is “Alaska Terrestrial and Marine Climate Trends, 1957–2021”, which was led by Tom Ballinger, Research Assistant Professor with the International Arctic Research Center at the University of Alaska Fairbanks. This paper has just been published in the American Meteorological Society’s Journal of Climate and should be open access, available here.

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What are the findings?

You can read the abstract and significance statement in Fig. 1. In a nutshell, Alaska is warming: there is significant regional and season variation but overall the warming exceeds regional increases in contiguous 48 states. Precipitation is increasing but the increases are not yet exceeding the typical year-to-year variability except on the North Slope. Snowfall is decreasing in the autumn and spring but increasing winter except in the southernmost regions is decreasing in all seasons. Sea ice extent is seasonally decreasing. These are all themes I hammer on regularly. And now there’s a peer-reviewed paper to back that up.

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More details

The papers presents results on trends for the period 1957-2021 for:

• Temperatures

  • Seasonal/Annual

  • Annual extremes (highest and lowest one percent)

• Precipitation

  • Seasonal/Annual

  • Annual extremes (highest one and five day totals)

• Snowfall

  • Seasonal/Annual

• Sea Ice Extent near Alaska

  • Seasonal/Annual

We used two different data sets for temperature and precipitation: the ERA5 reanalysis and the NOAA National Centers for Environmental Information (NCEI) NClimGrid. These two data sets use completely different methodologies to construct gridded (continuous) estimates of temperature and precipitation for all of Alaska. ERA5 is derived from a short term weather model that is run over and over again incorporating remote sensing and in-situ observations. The NCEI NClimGrid is an interpolation model using in-situ observations and a background climatology. Mostly for convenience, annual and seasonal analyses are presented at the regional scale using the 13 Alaska divisions first developed by UAF’s Peter Bieniek in 2014¹ and adopted in 2015 by NCEI. For trends of temperature and precipitation extremes and snowfall, only the ERA5 reanalysis was evaluated as there are no analogous datasets from NCEI. For sea ice, the Historical Sea Ice Atlas² was used for the 1957-78 period and the the National Snow and Ice Data Center’s Sea Ice Index version 3 for 1979-2021. We also used three different regression techniques to quantify the trend and illustrate the importance of the start date on the results of the trend analysis.

The differences between the ERA5 and NClimGrid datasets in regional temperature trends are small. The differences between the two datasets in regional precipitation trends are large. The sparse network of reliable precipitation in Alaska overall (and even more sparse in the 21st century), severe data quality issues related to the automation of climate observations and lack of effective quality control leave the NCEI interpolation based approach riddled with obvious errors, leaving ERA5 as the best source for evaluating multi-decade precipitation trends at the regional scale.

Having the best available estimates of environmental trends scale in Alaska is important for many purposes: from the tribal and community scale for adaptation planning and grant writing to the state and national scale to (ideally) help inform policy discussions and decisions.

This paper only scratches the surface of the kinds of environemntal change information that Alaskans regularly ask about. Changes in storminess and winds are high of the request list. Changes in the length and intensity of the warm season are important for everything from permafrost thaw to gardening and commercial agricultural interests. For those and more, stay tuned.

1. Bieniek, P. A., Walsh, J. E., Thoman, R. L., & Bhatt, U. S. (2014). Using climate divisions to analyze variations and trends in Alaska temperature and precipitation. Journal of Climate, 27(8), 2800-2818.

2. Walsh, J. E., Fetterer, F., Scott Stewart, J., & Chapman, W. L. (2017). A database for depicting Arctic sea ice variations back to 1850. Geographical Review, 107(1), 89-107.