By Rachel Lucas
According to current global estimates, the rate of heat building up on Earth over the past decade is equivalent to detonating about four Hiroshima atomic bombs worth of energy per second[i]. That means, to current date, we have accumulated a near 2.5 billion atomic bombs of heat since 1998.[ii]
This heat is transferring itself into our oceans and (now) melting glaciers. In the face of this, denial of human-caused climate change still manages to persist.[iii] And yet, when we look to the science behind it, we find that 99.9% of climate scientists agree: accelerated climate change is happening, and this acceleration is human caused.[iv] Climate change denial is a serious issue that endorses political inaction and ultimately procures long-term negative ecological and economic impacts, and the root of this denial starts with a misunderstanding of what is a natural cause, and what isn’t.
One common argument provided by deniers is, “Earth’s climate is designed to change. It’s a completely natural cycle”. Now, this claim isn’t wrong per se, but it is, however, inapplicable to the climate change we are currently witnessing. To understand this inconsistency, it helps to have a basic grasp of the main component controlling these natural climate cycles, what are known as the Milankovitch cycles. In short, the Milankovitch cycles are recurrent changes in the positioning of the Earth in relation to the sun caused by fluctuations in the actual shape of the Earth's orbit, the degree of Earth’s axial tilt towards or away from the sun; and the circular “wobble” on its axis as it circles around the sun in its gravitational orbit. These changes occur across large time scales, roughly 100,000 years, and bring the Earth, overall, closer to or farther away from the sun.
As the Earth's orbit changes, so too does the amount of sunlight Earth receives at different latitudes in different seasons. The amount of sunlight received in the summer at high northern latitudes over the North Atlantic and Arctic Oceans appears to be especially important to determining whether the Earth is in an ice age or not. When the northern summer sun is strong (i.e., Earth has an ellipsoid orbit bringing closer to the sun with increased axial tilt bringing more direct heat and light to the N. Hemisphere) the Earth tends to be in a warm period that lasts about 10,000 y. This melts away glacial ice (e.g., melting of Greenland ice sheet) causing massive freshwater release into the ocean followed by a 400 ft. sea level rise. When the northern summer sun is weak (i.e., Earth has a circular orbit and decreased axial tilt limiting the amount of light and heat in the N. hemisphere) ice sheets formed over winter in the N. Atlantic and Arctic Ocean don’t melt in the summer and slowly amass over time forming massive glaciers; this brings about the next ice age that lasts for about 100,000 y. In short, that’s the natural cycle: brief warm periods (about 10,000 y) followed by the slow build of an ice age that lasts for about 100,000 y.
Earth left its most recent ice age 11,000 y ago which means our warming period (should have) ended about 1,000 y ago. It is now in a phase with a more circular orbit and decreasing tilt that’s slowly decreasing light in the N. hemisphere in the summer time. With less light in N during summer, this means the Earth should be very slowly cooling again, not warming, which means current warming trends are completely off track from the natural cycle. Furthermore, the kind of heat build-up brought about by the Milankovitch cycles would occur over about 100,000 y; instead, we have increased this rate of occurrence to such an accelerated pace (about 4 atomic bombs detonated every second) that we have reduced this 100,000 y time span to about a century. This reduction in timescale is massive, and the only thing that could account for its acceleration is, unfortunately, us. But accepting this truth doesn’t have to mean the end of the world! Instead, it is pivotal to delving deeper into understand all of the variables affecting current climate change, especially oceanic processes, and to start making the changes necessary to mitigate its effects.
NASA/GISS graph combining positive and negative forcing and temperature for a clear picture of the natural cycle in comparison to the current anthropogenic forcing due to industrial processes. Source: http://ossfoundation.us
[i] Nuccitelli D, Way R, Painting R, Cook J, Church J, 2012 analyzing global heat data global heat data created by combining pentadal (5-year average) ocean heat content data to a depth of 2,000 meters from Levitus et al. (2012), and land, atmosphere, and ice heating data from Church et al. (2011).
[iii] Estimated 52% of Americans in 2014 believe that scientists don’t agree on climate change or its cause. Conducted by the Yale Project on Climate Change Communication. Source: http://environment.yale.edu/poe/v2014/
[iv] Poll reviewed more than 24,000 peer-reviewed articles on global warming published in 2013 and 2014 surveying over 70,000 scientists. Source: http://www.msnbc.com/msnbc/how-climate-change-deniers-got-it-very-wrong