Photo: Eric Huybrechts / Flickr

Recently an associate asked why I say a 30 percent reduction in emissions by 2020 is key to the 2℃ limit on global temperature rise set by the Intergovernmental Panel on Climate Change (IPCC).

There are three factors that must be considered in judging how much time the world has left to reduce emissions.

The first is the total carbon load we are emitting. There is strong agreement that starting from 1860, the allowable limit to stay below 2℃ is a thousand gigatons of carbon released into the atmosphere. We’ve already put out 515 gigatons. Most of that was emitted between 1970 and 2011. We now have less than 485 gigatons remaining. The current rate of emissions is still increasing as developing nations come online.

What the CO2 limit estimates do not include are emissions of other greenhouse gasses like CFCs and NOx and methane. These emissions are increasing rather than decreasing. We have sufficient and steadily improving science. With each improvement in understanding, we see the necessity for further, not fewer, reductions in allowable emissions estimates.

The second factor is the interruption of the carbon dioxide/oxygen cycle that has been in relative balance for millennia but is now producing a new increase in CO2. Most of this is agriculture and deforestation.

There is growing concern over ocean acidification (gradual lowering of pH from around 8.3 to around 8.1 — a roughly 30 percent reduction in alkalinity toward acidity). There is a serious collateral effect on marine ecosystems here. Plankton, marine flora and krill are not only at the base of the marine food chain, they are responsible for more than 50 percent of oxygen in the atmosphere. As the pH is altered, there is evidence that the marine carbon dioxide/oxygen system is also being altered.

Increased need for food production has increased nutrient runoff into marine ecosystems. This leads to “blooms” that consume oxygen and create “dead zones.” These oxygen-depleted areas are expanding around the globe.

The oceans are the planet’s greatest “heat sink,” taking up about 90 percent of solar radiant energy. This impacts ocean circulation. Circulation is both horizontal and vertical. The Arctic is a principle driver of ocean circulation and is warming 2 to 2.5 times faster than temperate latitudes as the albedo (the reflecting power of Earth’s surface) is lowered by the loss of ice cover. This is happening more rapidly than models predicted. Better models and further resolution of data is resulting in greater immediacy of concern.

The third major factor in setting a date for emissions reduction is the lag time to bring meaningful changes in net global emissions and emissions already in the pipeline. Coordinating global environmental policy is totally new and untested in human civilization. It has historically been difficult between individual nations. Unilateral interests, perceptions, fears and even traditions are all major stumbling blocks. This makes the Paris Agreement even more extraordinary. Even those pledged goals are less than what is needed to keep temperatures below 2℃ according to the World Bank; World Meteorological Organization (WMO); and others who look at the economic, social as well as just the environmental perspectives.

Today we see a major wrench placed into the gears of emissions progress. The Trump administration is systematically dismantling environmental regulations that monitor and control greenhouse gas emissions (GHGs). The U.S. produces over 20 percent of global emissions despite recent major reductions introduced by President Obama’s Clean Power Plan. A delay in those reductions will counter reductions made by all the other Paris Agreement signatories.

The three factors identified above are well understood and reported by national agencies and national academies of science around the world.

Now we come to more complicated factors that have the potential to be total game-changers. These are “tipping points” and “feedback loops.”

Russian research data are indicating that the Siberian ice shelf is warming even faster than the overall Arctic. Methane produced by permafrost melting and methane clathrates (dense deposits of methane trapped inside crystals) is increasing.

As a greenhouse gas, methane is more than 20 times stronger than CO2, even though it has a much shorter lifespan in the atmosphere. A surge in methane emissions has contributed to several previous paleo-extinction events in Earth’s history. None of the methane emissions in those extinction events took place as rapidly as we are witnessing in Siberia today. Early analysis led us to believe methane probably would not contribute to a sudden contribution to warming. Rapid changes taking place today suggests we need to look again and more closely.

We have also witnessed a 2 percent average reduction in ocean oxygen. What does that bode? Will it mean a plankton die off? Is the ocean dying? What about the oxygen that the ocean contributes to the atmosphere?

Today, the air we breathe is 21 percent oxygen. What if we experience a 2 percent loss in atmospheric oxygen? Simple… We begin to die. At present, the science can’t completely answer that question but is raising concerns.

This brings me to the precautionary principle and why a 30 percent reduction by 2020 is necessary to remain below 2℃. To achieve this, we have to weigh the consequences against delay and inaction.

In Russian roulette, one successful cycle changes the odds from 6 to 1, to 5 to 1. If we continue, the odds of death increase from 4 to 1, 3 to 1, and so on. The consequences are catastrophic, so we don’t play Russian roulette if we’re sane. The same happens as global warming increases the chances of “tipping points” and “feedback loops.” We don’t know precisely how many chambers there are in the gun, but we know that if any of them pops, it would be a real bummer.

The IPCC has suggested a 30 percent reduction in emissions between 2025 and 2035 as a range to keep below 2℃. The IPCC estimates are made from data generated over the previous 5 years. That means there is a big time lag before even making an estimate. Every model thus far has “underestimated” the real changes witnessed in subsequent field measurements. If we take this lag in mind, the precautionary principle requires the reduction of emissions sooner rather than later to allow even the smallest margin of error.

The current willful demolition of U.S. energy policy is now a significant driver of global warming and political backsliding. If we allow it, the next chamber in climate roulette will result in a surprise none of us can afford.

W. Douglas Smith is an environmental scientist, environmental diplomat, explorer, educator and a retired Senior Compliance Investigator for the U.S. Environmental Protection Agency, where he worked for 36 years.

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