Causes of the Global Warming Observed since the 19th Century

Measurements show that the Earth’s global-average near-surface temperature has increased by about 0.8℃ since the 19th century. It is critically important to determine whether this global warming is due to natural causes, as contended by climate contrarians, or by human activities, as argued by the Intergovernmental Panel on Climate Change. This study updates our earlier calculations which showed that the observed global warming was predominantly human-caused. Two independent methods are used to analyze the temperature measurements: Singular Spectrum Analysis and Climate Model Simulation. The concurrence of the results of the two methods, each using 13 additional years of temperature measurements from 1998 through 2010, shows that it is humanity, not nature, that has increased the Earth’s global temperature since the 19th century. Humanity is also responsible for the most recent period of warming from 1976 to 2010. Internal climate variability is primarily responsible for the early 20th century warming from 1904 to 1944 and the subsequent cooling from 1944 to 1976. It is also found that the equilibrium climate sensitivity is on the low side of the range given in the IPCC Fourth Assessment Report.

Fair Plan 8: Earth’s Climate Future—Pope Francis’ Population Mistake

Pope Francis wrote in his Encyclical Letter Laudato Si’: On Care for Our Common Home: “Instead of resolving the problems of the poor and thinking of how the world can be different, some can only propose a reduction in the birth rate.” … “To blame population growth instead of extreme and selective consumerism on the part of some is one way of refusing to face the issues.” Here, we test the hypothesis that population size does not matter. We do so in terms of the effect of the size of the human population on its emission of greenhouse gases. We find that the hypothesis is false = PO-PULATION MATTERS. Ceteris paribus, the larger the population of human beings on Planet Earth, the more difficult it will be to reduce, and finally eliminate, the emission of greenhouse gases by humanity and, thereby, constrain human-caused climate change = Anthropogenic Global Warming.

A Fair Plan to Safeguard Earth’s Climate. 3: Outlook for Global Temperature Change throughout the 21st Century

We apply Singular Spectrum Analysis to four datasets of observed global-mean near-surface temperature from start year to through 2012: HadCRU (to = 1850), NOAA (to = 1880), NASA (to = 1880), and JMA (to = 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.

A Revised Fair Plan to Safeguard Earth’s Climate

In our original study we crafted trajectories for developed and developing countries that phased-out greenhouse gas emissions during 2015-2065 such that the maximum global warming does not exceed the 2℃ threshold adopted by the UN Framework Convention on Climate Change, and the cumulative emissions for developed and developing countries are identical. Here we examine the effects of increasing the start year from 2015 to 2030 in 5-year intervals, and the phase-out period from 50 to 100 years in 10-year intervals. We find that phase-out during 2020-2100 is optimal. This phase-out increases the year of peak emission from 2015 to 2030 for developed countries and from 2042 to 2053 for developing countries. It also increases the time from peak emissions to zero emissions from 50 to 70 years for developed countries and from 23 to 47 years for developing countries. Both outcomes should facilitate agreement of the Revised Fair Plan by the UNFCCC.

A Fair Plan to Safeguard Earth’s Climate

A maximum global-mean warming of 2°C above preindustrial temperatures has been adopted by the United Nations Framework Convention on Climate Change to “prevent dangerous anthropogenic interference with the climate system”. Attempts to find agreements on emissions reductions have proved highly intractable because industrialized countries are responsible for most of the historical emissions, while developing countries will produce most of the future emissions. Here we present a Fair Plan for reducing global greenhouse-gas emissions. Under the Plan, all countries begin mitigation in 2015 and reduce greenhouse-gas emissions to zero in 2065. Developing countries are required to follow a mitigation trajectory that is less aggressive in the early years of the Plan than the mitigation trajectory for developed countries. The trajectories are chosen such that the cumulative emissions of the Kyoto Protocol’s Annex B (developed) and non-Annex B (developing) countries are equal. Under this Fair Plan the global-mean warming above preindustrial temperatures is held below 2°C.

A Simple Deconstruction of the HadCRU Global-Mean Near-Surface Temperature Observations

Previously we have used Singular Spectrum Analysis (SSA) to deconstruct the global-mean near-surface temperature observations of the Hadley Centre—Climate Research Unit that extend from 1850 through 2012. While SSA is a very powerful tool, it is rather like a statistical “black box” that gives little intuition about its results. Accordingly, here we use the simplest statistical tool to provide such intuition, the Simple Moving Average (SMA). Firstly we use a 21-year SMA. This reveals a nonlinear trend and an oscillation of about 60 years' length. Secondly we use a 61-year SMA on the raw observations. This yields a nonlinear trend. We subtract this trend from the raw observations and apply a 21-year SMA. This yields a Quasi-periodic Oscillation (QPO) with a period and amplitude of about 62.4 years and 0.11°C. This is the QPO we discovered in our 1994 Nature paper, which has come to be called the Atlantic Multidecadal Oscillation. We then subtract QPO-1 from the detrended observations and apply an 11-year SMA. This yields QPO-2 with a period and amplitude of about 21.0 years and 0.04°C. We subtract QPO-2 from the detrended observations minus QPO-1 and apply a 3-year SMA. This yields QPO-3 with a period and amplitude of about 9.1 years and 0.03°C. QPOs 1, 2 and 3 are sufficiently regular in period and amplitude that we fit them by sine waves, thereby yielding the above periods and amplitudes. We then subtract QPO-3 from the detrended observations minus QPOs 1 and 2. The result is too irregular in period and amplitude to be fit by a sine wave. Accordingly we represent this unpredictable part of the temperature observations by a Gaussian probability distribution (GPD) with a mean of zero and standard deviation of 0.08°C. The sum of QPOs 1, 2 and 3 plus the GPD can be used to project the natural variability of the global-mean near-surface temperature to add to, and be compared with, the continuing temperature trend caused predominantly by humanity’s continuing combustion of fossil fuels.

Fair Plan 7: Earth’s Climate Future = Humanity’s Choice

Earth’s climate future is in the hands of humanity. If emissions of greenhouse gases remain unabated, Earth’s climate will return to the climate of the Late Eocene, 35 million years ago, when sea level was 73 meters (240 feet) higher than today. Should that occur, many coastal cities around the world would be inundated. Moreover the Global Warming of this unabated Reference case will be comparable to the Global Warming from the Last Glacial Maximum 21,000 years ago to the beginning of the Holocene interglacial climate 11,000 years ago. However, this human-caused Global Warming would occur 50 times faster than that caused by nature. Alternatively, humanity can mitigate greenhouse-gas emissions to keep Global Warming below the 2&#176C maximum adopted by the United Nations Framework Convention on Climate Change “to prevent dangerous anthropogenic interference with the climate system”. This mitigation can either be done rapidly, as in the “80/50” Plan to reduce greenhouse-gas emissions 80% by 2050, or much more slowly, from 2020 to 2100, as in the Fair Plan to Safeguard Earth’s Climate. The Fair Plan is a compromise between doing nothing, as in the Reference case, and rapidly reducing greenhouse-gas emissions, as in the 80/50 Plan. Regardless of the Plan chosen to reduce greenhouse-gas emissions to keep Global Warming below the UNFCCC limit of 2&#176C (3.6&#176F), it should not be tantamount to our saying to one of our planetary spacecraft, Bon Voyage, call us when you get to your planetary destination. Rather, as with our spacecraft, the chosen climate-change policy should be monitored throughout the 21st century and Midcourse Corrections made thereto as needed to keep our “Climate Spacecraft” on track to achieve its “Climate Target”.