Berkeley Earth Temperature Averaging Process

Berkeley Earth Temperature Averaging Process
Link	http://berkeleyearth.org/pdf/berkeley-earth-averaging-process.pdf
Climate Change	Yes
Human Cause	Yes
Author(s)
Affiliation
Sponsors
Date	2012/04/23

Introduction

The study found that the global land mean temperature has increased by 0.911 ± 0.042 C since the 1950s

Description

A new mathematical framework is presented for producing maps and large-scale averages of temperature changes from weather station data for the purposes of climate analysis. This allows one to include short and discontinuous temperature records, so that nearly all temperature data can be used. The framework contains a weighting process that assesses the quality and consistency of a spatial network of temperature stations as an integral part of the averaging process. This permits data with varying levels of quality to be used without compromising the accuracy of the resulting reconstructions. Lastly, the process presented here is extensible to spatial networks of arbitrary density (or locally varying density) while maintaining the expected spatial relationships. In this paper, this framework is applied to the Global Historical Climatology Network land temperature dataset to present a new global land temperature reconstruction from 1800 to present with error uncertainties that include many key effects. In so doing, we find that the global land mean temperature has increased by 0.911 ± 0.042 C since the 1950s (95% confidence for statistical and spatial uncertainties). This change is consistent with global land-surface warming results previously reported, but with reduced uncertainty.

Authors=Robert Rohde, Judith Curry, Donald Groom, Robert Jacobsen, Richard A. Muller, Saul Perlmutter, Arthur Rosenfeld, Charlotte Wickham, Jonathan Wurtele
Author Organization Affiliation=BerkeleyEarth
Sponsors= Charles G. Koch Charitable Foundation, Novim Group, Lee and Juliet Folger Fund, Lawrence Berkeley National Laboratory,
William K. Bowes Jr. Foundation, Fund for Innovative Climate and Energy Research (created by Bill Gates), Ann and Gordon Getty Foundation  

Introduction

While there are many indicators of climate change, the long-term evolution of global surface temperatures is perhaps the metric that is both the easiest to understand and most closely linked to the quantitative predictions of climate models. It is also backed by the largest collection of raw data. According to the summary provided by the Intergovernmental Panel on Climate Change (IPCC), the mean global surface temperature (both land and oceans) has increased 0.64 ± 0.13 C from 1956 to 2005 at 95% confidence (Trenberth et al. 2007).

During the latter half of the twentieth century weather monitoring instruments of good quality were widely deployed, yet the quoted uncertainty on global temperature change during this time period is still ± 20%. Reducing this uncertainty is a major goal of this paper. Longer records may provide more precise indicators of change; however, according to the IPCC, temperature increases prior to 1950 were caused by a combination of anthropogenic factors and natural factors (e.g. changes in solar activity), and it is only since about 1950 that man-made emissions have come to dominate over natural factors. Hence constraining the post-1950 period is of particular importance in understanding the impact of greenhouse gases.

The Berkeley Earth Surface Temperature project was created to help refine our estimates of the rate of recent global warming. This is being approached through several parallel efforts to A) increase the size of the data set used to study global climate change, B) bring additional statistical techniques to bear on the problem that will help reduce the uncertainty in the resulting averages, and C) produce new analysis of systematic effects, including data selection bias, urban heat island effects, and the limitations of poor station siting. The current paper focuses on refinements in the averaging process itself and does not introduce any new data. The analysis framework described here includes a number of features to identify and handle unreliable data; however, discussion of specific biases such as those associated with station siting and/or urban heat islands will also be published separately.

Conclusion

The spatial structure of the climate change during the last century is shown in Figure 7 and found to be fairly uniform, though with greater warming over the high latitudes of North America and Asia, consistent with prior results (Hansen et al. 2010). We also show the pattern of warming since the 1960s, as this is the period during which anthropogenic effects are believed to have been the most significant. Warming is observed to have occurred over all continents, though parts of South America are consistent with no change. No part of the Earth’s land surface shows appreciable cooling.