Using data to attribute episodes of warming and cooling in instrumental records

Abstract

The observed global-warming rate has been nonuniform, and the cause of each episode of slowing in the expected warming rate is the subject of intense debate. To explain this, nonrecurrent events have commonly been invoked for each episode separately. After reviewing evidence in both the latest global data (HadCRUT4) and the longest instrumental record, Central England Temperature, a revised picture is emerging that gives a consistent attribution for each multidecadal episode of warming and cooling in recent history, and suggests that the anthropogenic global warming trends might have been overestimated by a factor of two in the second half of the 20th century. A recurrent multidecadal oscillation is found to extend to the preindustrial era in the 353-y Central England Temperature and is likely an internal variability related to the Atlantic Multidecadal Oscillation (AMO), possibly caused by the thermohaline circulation variability. The perspective of a long record helps in quantifying the contribution from internal variability, especially one with a period so long that it is often confused with secular trends in shorter records. Solar contribution is found to be minimal for the second half of the 20th century and less than 10% for the first half. The underlying net anthropogenic warming rate in the industrial era is found to have been steady since 1910 at 0.07-0.08°C/decade, with superimposed AMO-related ups and downs that included the early 20th century warming, the cooling of the 1960s and 1970s, the accelerated warming of the 1980s and 1990s, and the recent slowing of the warming rates. Quantitatively, the recurrent multidecadal internal variability, often underestimated in attribution studies, accounts for 40% of the observed recent 50-y warming trend. T he world's longest instrumental record of temperature, Central England Temperature (CET), began to be collected in 1659 in an area enclosed by Lancashire, London, and Bristol, a few years after the invention of sealed liquid thermometers. It is the only instrumental record that extends back to the Little Ice Age (LIA), a period of cold climate in Europe, and the time of the Maunder Minimum, when sunspots vanished almost entirely for 70 y (1). The record then covers several subsequent episodes of natural and anthropogenic warming of multidecadal durations. Manley (2) painstakingly compiled most of the early monthly CET series, and Parker et al. (3) the daily data from 1772. Both are updated to present by the Met Office Hadley Centre. This record has previously been analyzed to study interannual and interdecadal variability up to the 25-y period (4); interannual winter variability and its association with solar forcing (5); and its variance at interannual, interdecadal timescales compared with a general circulation model output (6). The lower frequency portion of the record, longer than 50 y, has not been adequately analyzed, the difficulty being that even this long record is not long enough to avoid the cone of influence from the edges of the time series. Her...

Statistically derived contributions of diverse human influences to twentieth-century temperature changes

“…This natural multidecadal oscillation, superimposed on a secular warming trend, is proposed for explaining the non-monotonic warming shown by global temperatures during the 20th century, including the cooling of the mid-century and the recent slowdown in the warming. The authors argue that the warming trend has remained almost constant since 1910 at 0.07-0.08 °C/decade 48 . The most significant differences between the results from these papers and those presented here can be attributed to the use of a linear trend to represent the warming trend, as well as to the lack of testing for breaks in the trend function.…”

“…Two recent papers 48,49 are related to the present study, in the sense that they use a similar regression-based approach to filter the effects of AMO from global temperatures in order to extract a clearer warming signal from the data. Nevertheless, the estimates and interpretation of the warming trend and of its nonlinearities are very different to those presented here.…”

Imprint of the Atlantic multi-decadal oscillation and Pacific decadal oscillation on southwestern US climate: past, present, and future

“…Semenov et al (2010) estimated the AMO contribution to post 1970 global warming to be 0.24°C. Tung and Zhou (2013) found that neglecting the AMO leads to an overestimation of the global mean anthropogenic warming trend during the second half of the twentieth century by about a factor of two. Hansen et al (http://www.columbia.edu/*jeh1/mailings/ 2013/20130115_Temperature2012.pdf) suggested that natural variability is responsible for over a decade of stable global mean temperatures since about 2000.…”

“…The global climate change is driven by increasing atmospheric concentration of greenhouse gases (GHGs) as well as by natural climate variability (Wu et al 2007(Wu et al , 2011aTung and Zhou 2013). While the warming by increasing GHGs is well captured by climate models (Solomon et al 2007), the treatment of natural variability remains a challenge (Dai et al 2005;Zhang et al 2007;Solomon et al 2011;Wyatt et al 2011).…”

500-year climate cycles stacking of recent centennial warming documented in an East Asian pollen record

“…Observations and model simulations over recent centuries suggested that multidecadal to multicentennial cyclic change of solar activity and climate patterns (such as Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, and North Atlantic Deep Water) still existed under anthropogenic forcing and played an important role in regulating global to regional terrestrial (EA, North America, and Europe) and marine (North Atlantic and Pacific) climate change during the past centuries [9][10][11][12][13][14][15] . But recent studies based on global and regional climate records indicated that the warming of the past century is unprecedented and not relative to natural forcing but anthropogenic forcing 4,16,17 .…”