Michael E. Schlesinger, Daniela Lindner, Michael J. Ring, Emily F. Cross
Climate Research Group, Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, USA.
DOI: 10.4236/jep.2013.46075   PDF    HTML   XML   4,727 Downloads   7,925 Views   Citations

Abstract

We apply Singular Spectrum Analysis to four datasets of observed global-mean near-surface temperature from start year t_o through 2012: HadCRU (t_o = 1850), NOAA (t_o = 1880), NASA (t_o = 1880), and JMA (t_o = 1891). For each dataset, SSA reveals a trend of increasing temperature and several quasi-periodic oscillations (QPOs). QPOs 1, 2 and 3 are predictable on a year-by-year basis by sine waves with periods/amplitudes of: 1) 62.4 years/0.11°C; 2) 20.1 to 21.4 years/0.04°C to 0.05°C; and 3) 9.1 to 9.2 years/0.03°C to 0.04°C. The remainder of the natur°l variability is not predictable on a year-by-year basis. We represent this noise by its 90 percent confidence interval. We combine the predictable and unpredictable natural variability with the temperature changes caused by the 11-year solar cycle and humanity, the latter for both the Reference and Revised-Fair-Plan scenarios for future emissions of greenhouse gases. The resulting temperature departures show that we have moved from the first phase of learning—Ignorance—through the second phase—Uncertainty—and are now entering the third phase—Resolution—when the human-caused signal is much larger than the natural variability. Accordingly, it is now time to transition to the post-fossil-fuel age by phasing out fossil-fuel emissions from 2020 through 2100.

Keywords

Climate Change; Global Warming; Greenhouse-Gas Emissions; Mitigation

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1. Introduction

In our year-2000 “Causes of Global Temperature Changes During the 19^th and 20^th Centuries” paper we concluded: “Accordingly, it is prudent not to expect year-after-year warming in the near future and, in so doing, diminish concern about global warming should global cooling instead manifest itself again (as it did from 1944 to 1976)” [1] (hereafter Causes 1). This caution notwithstanding, some climate skeptics have concluded that there is no human-caused global warming because during the time period 1998 to 2008, there was no increase in the globalmean near-surface temperature [2]. In our 2012 paper, “Causes of the Warming Observed Since the 19^th Century” [3] (hereafter Causes 2), we showed that the absence of warming during 1998-2008 was the result of natural cooling counteracting the human-caused warming. Recently Andy Revkin, author of the Dot Earth blog on the NY Times website [4], emailed us “… but if the “pause” (in global warming) persists through 2017 or longer (absent some obvious push like eruptions), that could raise questions (about the reality of human-caused warming) [5].”

Accordingly, in this paper we examine the issue of future naturally occurring variability in the Earth’s climate system in comparison with human-caused global warming. To do so we will analyze the observed changes in Earth’s global-mean near-surface temperature from 1850 to 2012 to project future temperature changes through 2100. We will combine this natural variability, both predictable year-by-year and unpredictable year-by-year, with the human-caused changes in global-mean nearsurface temperature for the Reference and Mitigation scenarios of our two 2012 papers, “A Fair Plan to Safeguard Earth’s Climate [6] (hereafter FP1) and a “Revised Fair Plan to Safeguard Earth’s Climate” [7] (hereafter FP2). In so doing we shall show that the time when natural variability in the Earth’s climate system could counterbalance human-caused global warming is coming to an end because humanity has now become the dominant shaper of Earth’s future climate. We shall thereby show, yet again as we did in FP2, that unless humanity reduces its emission of greenhouse gases to zero from 2020 through 2100, the rise in global-mean near-surface temperature will exceed the 2˚C (3.6˚F) limit adopted by the UN Framework Convention on Climate Change “to prevent dangerous anthropogenic interference with the climate system” [8,9].

2. Analysis of the Observed Changes in Global-Mean Near-Surface Temperature, 1850 through 2012

The observed changes in global-mean near-surface temperature are due to two factors, one external to the climate system, and the other internal thereto. The external factors influence climate but are not influenced by climate. These include variations in solar irradiance and volcanoes. The internal factors influence climate and are influenced by climate. These include the interactions among the components of the climate system—the atmosphere, ocean, cryosphere, geosphere and biosphere— and human changes to the climate system.

In 1994, we published our first paper analyzing the observed changes in global-mean near-surface temperature, “An Oscillation in the Global Climate System of Period 65 - 70 Years” [10]. Therein we used a then recently developed method of spectral analysis called Singular Spectrum Analysis (SSA). In SSA the mathematical structures (basis functions) onto which the observed temperature departures from the 1961-1990 mean temperature are projected, are not prescribed (usually trigonometric functions) but instead are determined by the observed temperatures themselves. Doing this allows SSA to find statistically significant structures in the data that ordinary Fourier analysis cannot. Because of this we discovered a 65 - 70 year oscillation in the global-mean near-surface temperature record that was due to an oscillation in the near-surface temperature over the North Atlantic Ocean. This oscillation has come to be known as the Atlantic Multidecadal Oscillation (AMO). It is this AMO that caused the early twentieth century warming (1904 to 1944) and subsequent mid-twentieth century cooling (1944 to 1976) [1,3,10]. It is the latter that caused us to write the cautionary warning stated in the Introduction.

2.1. Observed Global-Mean Near-Surface Temperature Data

We shall not elaborate the mathematics of SSA here, as we have thoroughly done so in our earlier papers [1,3, 10]. We do note however that we no longer use our Simple Climate Model [1,10,11] to detrend the observed record of global-mean near-surface temperatures before applying SSA, as we did in our 1994 and 2000 (Causes 1) papers [1,10]. Rather, we determine this trend by SSA itself and, thereby, do not impose a model on the data before applying SSA thereto. We first did this in our Causes 2 paper [3]. In that paper we analyzed the observed near-surface temperature records of the four groups that annually provide these data, namely: 1) the Hadley Centre-Climate Research Unit (HadCRU) located in the United Kingdom, with data starting in 1850 [12]; 2) the National Climate Data Center of the US National Oceanographic and Atmospheric Administration (NOAA) located in Asheville, North Carolina, with data starting in 1880 [13]; 3) the Goddard Institute of Space Studies of the US National Aeronautics and Space Administration (NASA) located in New York City, with data starting in 1880 [14]; and 4) the Japanese Meteorological Agency (JMA) located in Tsukuba, Japan, with data starting in 1891 [15,16]. We shall see that the start dates of the NOAA, NASA and JMA datasets are too late to correctly determine the structure of the AMO, the most important variation in the four datasets. In our Causes 2 paper we analyzed these four observational datasets through 2010. Here we add two more years of data—2011 and 2012.

Figure 1 shows the four observed global-mean nearsurface temperature departures from the 1961-1990 average temperature (black line), together with their SSAdetermined trend (red line). As we showed in our Causes 2 paper, the global-warming trend determined by SSA is caused by humanity through: 1) the release of carbon dioxide (CO₂) by the burning of fossil fuels: coal, natural gas and oil; 2) the release of methane (CH₄) by flatulent livestock animals in animal husbandry, coal mining and land fills; 3) nitrogen dioxide (N₂O) by the use of nitrogen-rich fertilizer in agriculture to replenish the nitrogen taken out of the soil and fixed in agricultural biomass; and 4) the release of human-made chloroflurocarbons (CFCs) used as spray propellants and refrigerants. It is evident from Figure 1 that there is a rich variability in the global-mean near-surface temperature in addition to the human-caused global warming from the mid 19^th century to the present.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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