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Improvements in the uncertainty model in the Goddard Institute for Space Studies Surface Temperature (GISTEMP) analysis

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We outline a new and improved uncertainty analysis for the Goddard Institute for Space Studies Surface Temperature product version 4 (GISTEMP v4). Historical spatial variations in surface temperature anomalies are derived from historical weather station data and ocean data from ships, buoys, and other sensors. Uncertainties arise from measurement uncertainty, changes in spatial coverage of the station record, and systematic biases due to technology shifts and land cover changes. Previously published uncertainty estimates for GISTEMP included only the effect of incomplete station coverage. Here, we update this term using currently available spatial distributions of source data, state‐of‐the‐art reanalyses, and incorporate independently derived estimates for ocean data processing, station homogenization, and other structural biases. The resulting 95% uncertainties are near 0.05 °C in the global annual mean for the last 50 years and increase going back further in time reaching 0.15 °C in 1880. In addition, we quantify the benefits and inherent uncertainty due to the GISTEMP interpolation and averaging method. We use the total uncertainties to estimate the probability for each record year in the GISTEMP to actually be the true record year (to that date) and conclude with 87% likelihood that 2016 was indeed the hottest year of the instrumental period (so far).
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Improvements in the GISTEMP Uncertainty Model
Nathan J. L. Lenssen1,2 , Gavin A. Schmidt1, James E. Hansen3, Matthew J. Menne4,
Avraham Persin1,5, Reto Ruedy1,5, and Daniel Zyss1
1NASA Goddard Institute for Space Studies, New York, NY, USA, 2Department of Earth and Environmental Sciences,
Columbia University, New York, NY, USA, 3Climate Science, Awareness and Solutions, Columbia University Earth
Institute, New York, NY, USA, 4NOAA National Centers for Environmental Information, Asheville, NC, USA, 5SciSpace
LLC, New York, NY, USA
Abstract We outline a new and improved uncertainty analysis for the Goddard Institute for Space
Studies Surface Temperature product version 4 (GISTEMP v4). Historical spatial variations in surface
temperature anomalies are derived from historical weather station data and ocean data from ships, buoys,
and other sensors. Uncertainties arise from measurement uncertainty, changes in spatial coverage of the
station record, and systematic biases due to technology shifts and land cover changes. Previously published
uncertainty estimates for GISTEMP included only the effect of incomplete station coverage. Here, we
update this term using currently available spatial distributions of source data, state-of-the-art reanalyses,
and incorporate independently derived estimates for ocean data processing, station homogenization, and
other structural biases. The resulting 95% uncertainties are near 0.05 C in the global annual mean for the
last 50 years and increase going back further in time reaching 0.15 C in 1880. In addition, we quantify the
benefits and inherent uncertainty due to the GISTEMP interpolation and averaging method. We use the
total uncertainties to estimate the probability for each record year in the GISTEMP to actually be the true
record year (to that date) and conclude with 8 % likelihood that 2016 was indeed the hottest year of the
instrumental period (so far).
1. Introduction
Attempts to seriously estimate the changes in temperature at the hemispheric and global scale date back at
least to Callendar (1938) who used 147 land-based weather stations to track near-global trends from 1880
to 1935 (Hawkins & Jones, 2013). Subsequent efforts used substantially more data (180 stations in Mitchell,
1961; 400 stations in Callendar, 1961; “several hundred” in Hansen et al., 1981; etc.), and with a greater
global reach. While efforts were made to estimate the uncertainty associated with these products, they were
more suggestive than comprehensive.
As the data sets have grown in recent years (through digitization and synthesis of previously separate data
streams; Freeman et al., 2016; Rennie et al., 2014; Thorne et al., 2018), and efforts have been made to improve
data homogenization, bias corrections, and interpolation schemes, the sophistication of the uncertainty
models has also grown. Notably, with the introduction of the Hadley Centre sea surface temperature (SST)
analysis HadSST3 (Kennedy et al., 2011a, 2011b), Berkeley Earth (Rohde et al., 2013a), and the joint Hadley
Centre and University of East Anglia's Climatic Research Unit Hadley Centre/Climatic Research Unit 4
(HadCRUT4; Morice et al., 2012), Monte Carlo methodologies have been applied to generate observational
ensembles that quantify uncertainties more comprehensively than was previously possible.
Goddard Institute for Space Studies Surface Temperature (GISTEMP) is a widely used data product that
tracks global climate change over the instrumental era. However, the existing uncertainty analysis cur-
rently contains only rough estimates of uncertainty on the land surface air temperature (LSAT) mean and
no estimates of the SST or total (land and sea surface combined) global mean. This paper describes a new
end-to-end assessment of all the known uncertainties associated with the current GISTEMP analysis (nom-
inally based in the methodology described in Hansen et al., 2010, but with changes to data sources as
documented on the GISTEMP website and outlined below), denoted as version 4. We use independently
derived uncertainty models for the land station homogenization (Menne et al., 2010, 2018) and ocean tem-
perature products (Huang et al., 2015, 2017), combined with our own assessment of spatial interpolation
and coverage uncertainties, as well as parametric uncertainty in the GISTEMP methodology itself.
RESEARCH ARTICLE
10.1029/2018JD029522
Key Points:
• A total uncertainty analysis for
GISTEMP is presented for the first
time
• Uncertainty in global mean surface
temperature is roughly 0.05
degrees Celsius in recent decades
increasing to 0.15 degrees Celsius in
the nineteenth century
• Annual mean uncertainties are small
relative to the long-term trend
Correspondence to:
N. J. L. Lenssen,
n.lenssen@columbia.edu
Citation:
Lenssen, N. J. L., Schmidt, G. A.,
Hansen, J. E., Menne, M. J., Persin, A.,
Ruedy, R., & Zyss, D. (2019).
ImpImprovements in the GISTEMP
uncertainty model. Journal of
Geophysical Research: Atmospheres,
124, 6307–6326. https://doi.org/10.
1029/2018JD029522
Received 23 AUG 2018
Accepted 12 MAY 2019
Accepted article online 23 MAY 2019
Published online 24 JUN 2019
Corrected 27 AUG 2019 and
28 FEB 2020
This article was corrected on
2019 and 28 FEB 2020. See the end
of the full text for details.
©2019. American Geophysical Union.
All Rights Reserved.
LENSSEN ET AL. 6307
7
27 AUG
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