Saving Earth’s Refrigerator: what does global warming mean for our planet’s future?

Back in 1988, Jim Hansen of NASA told the United States Congress that the global warming of recent years was due to the burning of fossil fuels, which added so much dioxide (CO₂) to the atmosphere that it exacerbated the greenhouse effect that kept the planet naturally warm. This new global warming was causing changes to climate and weather. It was greater in high latitudes than in low, and greater over land than over the ocean. With the benefit of hindsight, it’s clear that the continued increase in atmospheric CO₂ from 350 ppm in 1988 to 412 ppm in 2022 is due to the fact that, since 1950, we have burned more than 90% of all the fossil fuel ever burned.

We have also learned that increases in other greenhouse gases emitted by human activities—like methane (CH₄), nitrous oxide (N₂O), and the chlorofluorocarbons (CFCs)—have added to the CO₂-induced warming. Their effect is calculated by converting them to the equivalent amount of CO₂, then adding that to the actual CO₂ abundance to give the effective CO₂. According to the National Oceanic and Atmospheric Administration (NOAA), this is at about 500 ppm—a lot more than the 412 ppm due to CO₂ alone. No wonder we are warming up.

Global temperature increase means melting snow and ice caps

 Hansen was right. Although the global average temperature increase above the average for 1850-1900 is now almost 1.2ºC, it is close to 1ºC over the ocean, 2ºC over land, and about 3.6ºC over the Arctic. The Arctic is where much of the threat of global warming originates, because that’s where we have the most ice and snow in the Northern Hemisphere. We also find ice and snow in the Antarctic and in what scientists refer to as the “Third Pole,” the high mountains. In these three places, ice and snow are melting away as the world warms.

One key result is that sea level is rising. It rose about 20cm since the 1850-1900 baseline period but is happening at an increasing rate and is now 4 mm a year. Continued ice and snow melt may cause global sea level to reach between 1.5 m and 2 m by the end of the century, and 15 m by the year 2300. Although that estimate may seem extraordinary, geological data show that during periods of natural warming sea levels did rise by such amounts—for instance, 3 million years ago in Pliocene time, CO₂ levels were in the range 450-500 ppm.

Melting snow and ice means losing Earth’s albedo

My lecture audiences are not surprised that global warming melts ice and snow and makes sea levels rise. But they are surprised to learn that this same melt adds to the warming. This happens because ice and snow reflect solar energy. By doing so they keep our climate moderately cool. They are acting as Earth’s Refrigerator. As they melt away we are losing that reflectivity (Earth’s albedo). It’s as if we have gone away on vacation and accidentally left our fridge door open; everything inside begins to rot. Instead of that energy being reflected to outer space, it warms the ground and the ocean, which emit heat that is absorbed by the greenhouse gases. This creates a climate double whammy: warming caused by our CO₂ emissions plus warming added by the loss of albedo. As mentioned earlier, CO₂ is not acting alone. It is aided and abetted in particular by emissions of methane (CH₄). In addition the warming created by these gases is exacerbated by water vapour, which evaporates from the warming ocean and is a powerful greenhouse gas in its own right. 

Greenland is losing ice by melting at its surface. Antarctica is much colder, and very little of its ice is melting at the surface of its vast ice sheet. However, the Southern Ocean around the continent is warming, and its warm water is penetrating beneath the ice shelves that surround the continent, melting them from beneath. The net result is that both Greenland and Antarctica have lost about 5,000 billion tonnes of ice since 1980. Between 1993 and 2018, 8% of sea level rise came from Antarctic melt, 15% from Greenland, 21% from mountain glaciers, and 42% from the thermal expansion of heated seawater; the rest came from the pumping of groundwater for agriculture.

One of the most dramatic indicators of global warming is the loss of sea ice from the Arctic Ocean, which is likely to be ice-free in the summer by 2050. The volume of ice, as well as its area has diminished; since the late 1970s nearly all of the sea ice between 1 m and 6 m thick has disappeared. While this has not changed sea level, it did contribute to the shrinking of Earth’s Refrigerator.

Loss of ice means habitat erosion and extreme weather

Our planetary ice cover is extremely important. Mountain ice forms water towers for nearby populations. As it melts away, so does their water supply. Arctic snow and ice provide habitats for wildlife. As it melts away, those habitats shrink. As the Arctic warms, rain replaces snowfall and turns to ice at the surface, making it difficult for reindeer to feed. As the sea ice melts away from Arctic coasts, waves erode beaches and settlements. As Antarctic sea ice melts, penguin populations shift.

Away from icy regions, global warming dries vegetation and soils in already dry areas, making them more prone to wildfires. When the temperature over the ocean increases by just 1ºC, you get 7% more evaporation, which, when moist marine air hits land, means a lot more flooding in traditionally wet areas.

How can we save Earth’s Refrigerator?

Evidently, anything we can do to eliminate global warming would help us to escape from these various dire side effects. Can we save Earth’s Refrigerator? Much mentioned is the concept of Net Zero, which means taking out from the air as much CO₂ as we add to it. This is a tricky thing to do at the best of times. But in a very real sense it is an illusion, because it would mean maintaining in the air the current level of CO₂, which would lead to continued warming, ice loss, and sea level rise.

What we really need are, firstly, fewer emissions, and, secondly, “negative emissions”—multiple means for extracting vastly more CO₂ than we continue to supply. Without “negative emissions” we will hit an average global warming of well over 2ºC this century, which means well over 4ºC in the polar regions, hence vastly more ice and snow melt. To stop ice and snow melt we must also somehow increase the reflective effects of ice and snow. This could be done in the Arctic, for example, by pumping seawater into the air to stimulate the formation of reflective cloud cover. None of this will be cheap. But if we want our grandchildren and their descendants to experience the same equable climate through which our civilization developed, we have no choice but to work to save Earth’s Refrigerator.

_{Featured image by Michael Fenton, via Unsplash (public domain)}