How Should We Assess Global Warming?

Highly qualified scientists, economists, and other scholars vigorously debate global warming and what, if anything, to do about it. A Christian understanding of the issue must integrate well-informed input from many disciplines, including philosophy, theology, ethics, natural sciences, and social sciences. Brevity requires this article consider only a few.

Importantly, ethical guidelines for researching the matter require that all participants must be committed to truth and ready to reconsider assumptions in light of new evidence or reasoning—this practice is the key to conducting good science (1Th 5:21). They must avoid logical fallacies, especially ad hominem attacks on those with whom they disagree. They must not, as e-mails released in the “Climategate” scandal revealed (Montford, Hiding the Decline, 2012), fabricate, falsify, or exaggerate support data, suppress opposing data, intimidate scholars with contrary views, or try to end debate.

Causes proposed for global warming may be categorized as either natural or anthropogenic (resulting from human influence on the natural world). Among natural causes are solar, galactic, geologic, and oceanic cycles of varying and overlapping periodicities, meaning that a first step toward understanding recent and future changes in global average temperature (GAT) is recognizing that it has risen and fallen repeatedly throughout geologic history (Singer & Avery, Unstoppable Global Warming, 2007). Notably, recent changes in current warming have not exceeded past increases in rate or magnitude.

Among anthropogenic causes are deforestation and the burning of fossil fuels like coal, oil, and natural gas to produce energy. These practices increase atmospheric carbon dioxide (CO2), which is the second most important “greenhouse gas” concentration. (About 95 percent of the “greenhouse effect”—the warming of earth’s atmosphere—comes from water vapor and clouds, 4.5 percent is attributed to CO2, and the remaining 0.5 percent comes from methane and several trace gases.) Importantly, “greenhouse gas” is a misnomer. Glass enclosure traps air warmed by sunlight [energy in the visible light spectrum] from rising. Greenhouse gases warm the atmosphere by absorbing and radiating heat [energy in the infrared spectrum reflecting from earth’s surface], sending some back toward earth’s surface. Since pre-industrial times, concentration of atmospheric CO2 has risen approximately 43 percent.

As for magnitude, GAT has risen about one degree centigrade since 1850. Doubling atmospheric CO2 concentration would by itself probably increase it that much or a bit more, probably bringing more benefits than harms. Fears of dangerous warming, in fact, rest on theories about how other elements of the climate system might magnify that warming through things like increasing evaporation that would increase water vapor. Some climate scientists attempt to estimate those possibilities with computer models, a difficult task because our understanding of many feedbacks is severely limited.

The models yield estimates of equilibrium climate sensitivity (ECS) of ~1.5–4.5°C with “best estimate” of 3.0°C. However, models have predicted, on average, two to three times observed warming over the relevant period; 95 percent have predicted more warming than observed, indicating that errors are not random but driven by accidental or intentional bias; and none predicted the complete absence of statistically significant warming from early 1997 to late 2015. These facts suggest that the models are unreliable. As time passes and empirical observations correct them, estimates of ECS yield lower ranges, like ~0.3–1.0°C (NIPCC, 2013a, p. 7), or ~1.25–3.0°C with a best estimate of ~1.75°C (Lewis and Crok, A Sensitive Matter, 2013).

Biblical revelation offers another ground for low estimates of ECS. High estimates assume the climate system is extremely fragile, subject to catastrophic consequences from a comparatively tiny cause, which is difficult to reconcile with the understanding that earth and all its subsystems are the product of an infinitely wise and powerful Creator who faithfully sustains them (Gn 1:31; 8:22; Ps 104:6-9).

Assessing risks of anthropogenic global warming (AGW) adds new uncertainties. Claims that AGW will cause accelerated sea level rise; more frequent and severe extreme weather events like hurricanes, tornadoes, floods, droughts, and heat waves; spread of tropical diseases; accelerating species extinctions; and conflict over natural resources, though common, are not well supported empirically. A common-sense objection to high risks from AGW even toward the upper end of IPCC’s ECS estimate is that local temperatures vary by two to twenty times as much daily and ten to forty times as much annually without catastrophic results. Also, the costs of AGW must be weighed against the benefits of the activities that drive it—reduction of poverty by economic production energized by fossil fuel use and the improvement of plant growth and hence agricultural productivity. Numerous studies find that the risks of human poverty far outweigh climate and weather-related risks, so as societies get wealthier, their people can adapt better to any future climate. Also, empirical studies demonstrate that doubled atmospheric CO2 concentration yields an average 35 percent increase in plant growth efficiency, with plants growing better in warmer and cooler temperatures and in wetter and drier soils, making better use of soil nutrients, and resisting diseases and pests better, thus expanding their range and density, “greening” the earth, and improving fruit to fiber ratios, and making more food available and benefiting the poor most of all.

Finally, determining best responses to ECS requires careful cost/benefit analysis (counting not only narrowly defined economic measures like gross domestic product but also broader measures like human and ecosystem health) fraught with its own uncertainties. For instance, while full compliance with the global climate treaty adopted in Paris in 2015 is estimated to cost of over $80 trillion to reduce GAT in 2100 by ~0.17°C (Lomborg, “Gambling the World Economy on Climate,” WSJ, 2015; “Impact of Current Climate Proposals,” Global Policy, 2015), that temperature difference, and any benefits of it, would shrink if ECS is lower than the IPCC’s estimate. Also, IPCC projects that today’s poor societies become healthier and wealthier one and two centuries from now in warmer than in cooler scenarios because in its models fossil fuel use drives economic growth, which drives warming (Goklany, “Is Global Warming the Number One Threat to Humanity,” 2012). This implies that reducing global warming by reducing fossil fuel use not only does more harm than good but also requires poorer people today to sacrifice for the sake of richer people of the future, an intergenerational injustice.

For competing evangelical views on global warming, see Cornwall Alliance for the Stewardship of Creation (www.CornwallAlliance.org) and Evangelical Environmental Network (www.CreationCare.org).