When politicians talk about achieving “net zero” emissions, they are often relying on trees or technology which can extract carbon dioxide from the air. What they don’t mention is how much these proposals or geoengineering would cost to keep the world burning fossil fuels.
There are many proposals for removing carbon dioxide, but most only make marginal differences, and carbon dioxide concentrations in the atmosphere have continued to rise unabated even during the pandemic.
I was working on climate change for more than four decades. Let’s take a minute to understand some of the rhetoric around climate change and clear the air, so to speak.
What causes climate change?
When fossil fuels are burned to produce energy or used in transportation, they release carbon dioxide – a greenhouse gas that is the main cause of global warming. Carbon dioxide stays in the atmosphere for centuries. As more and more carbon dioxide is added, its increasing concentration acts as a blanket, trapping energy near the Earth’s surface that would otherwise escape into space.
When the amount of energy coming from the Sun exceeds the amount of energy reflected back into space, the climate warms. Some of this energy increases temperatures, and some increases evaporation and fuels storms and rains.
Due to these changes in the composition of the atmosphere, the planet has warmed by about 1.1 degrees Celsius (2 F) since about 1880 and is well on its way to 1.5 C (2.7 F), which has been highlighted as a goal not to be crossed if possible by the Paris Agreement. With global warming and gradual increases in temperature, there have been increases in all kinds of weather and climate extremesfrom floods to droughts and heat waves, which cause enormous damage, disruption and loss of life.
Studies show that global carbon dioxide emissions will have to achieve net zero carbon emissions by mid-century have a chance of limiting warming to even 2 C (3.6 F).
Currently, the main source of carbon dioxide is China. But accumulated emissions matter most, and the United States leads, followed closely by Europe, China and others.
What works to slow climate change?
Modern society needs energy, but it doesn’t have to come from fossil fuels.
Studies show that the the most effective way to fight climate change problem is to decarbonize the economies of the nations of the world. This means a big increase in the use of renewable energy – solar and wind cost less than new fossil fuel power plants in much of the world today – and the use of electric vehicles.
Unfortunately, this shift to renewables has been slow, largely due to the huge and expensive fossil fuel infrastructure, as well as the large amount of dollars that can buy influence from politicians.
Instead of drastically reducing emissions, companies and politicians have seized on alternatives. These include geoengineering; carbon capture and storage, including “direct aerial capture”; and to plant trees.
Here is the problem:
Geoengineering often stands for “solar radiation management”, which aims to mimic a volcano and add particles to the stratosphere to reflect incoming solar radiation back into space and produce cooling. This might partially work, but it might have about side effects.
The problem with global warming is not the sun, but rather the fact that the infrared radiation emitted by the Earth is trapped by greenhouse gases. Between incoming and outgoing solar radiation lies the entire weather and climate system and the hydrological cycle. Sudden changes in these particles or maldistribution could have dramatic effects.
The last major volcanic eruption, that of Mount Pinatubo in 1991, sent enough sulfur dioxide and particulate matter into the stratosphere to produce modest cooling, but it also caused a loss of precipitation on the land. It cooled the land more than the ocean, so the monsoon rains moved offshore, and in the longer term it slowed the water cycle.
Carbon capture and storage has been researched and tested for over a decade, but considerable costs. Only about a dozen industrial plants in the United States currently capture their carbon emissions, and most of it is used to improve oil drilling.
Direct air capture – a technology that can extract carbon dioxide from the air – is being developed in several places. It uses a lot of energy, however, and even though it might potentially be processed using renewable energyit’s still energy-intensive.
Planting trees is often seen as a solution to offset corporate greenhouse gas emissions. Trees and vegetation absorb carbon dioxide through photosynthesis and produce wood and other plant matter. It’s relatively cheap.
But trees are not permanent. Leaves, twigs and dead trees rot. The forests are burning. Recent studies show that the risks for trees stress, wildfires, drought and insects as temperatures rise will also be greater than expected.
How much does all this cost?
Scientists have been measuring carbon dioxide at Mauna Loa, Hawaii, since 1958 and elsewhere. The average annual increase in carbon dioxide concentration has accelerated from about 1 part per million volume per year in the 1960s to 1.5 in the 1990s, to 2.5 in recent years since 2010.
This relentless increase, through the pandemic and despite the efforts of many countries to reduce emissions, shows how enormous the problem is.
Usually, carbon removal is discussed in terms of mass, measured in megatons — millions of metric tons — of carbon dioxide per year, not parts per million volume. The mass of the atmosphere is about 5.5×1015 metric tons, but since carbon dioxide (molecular weight 42) is heavier than air (molecular weight about 29), 1 part per million volume of carbon dioxide carbon is approximately 7.8 billion metric tons.
According to the World Resources Institute, the cost range for direct air capture vary between US$250 and US$600 per metric ton of carbon dioxide removed today, depending on technology, energy source and scale of deployment. Even though costs have fallen to $100 per metric ton, the cost of reducing atmospheric carbon dioxide concentrations by 1 part per million is about $780 billion.
Keep in mind that the concentration of carbon dioxide in the atmosphere has increased by about 280 parts per million pre-industrial era to around 420 today, and it is currently increasing to more than 2 parts per million per year.
According to WRI calculations, restoring trees on one-third to two-thirds of suitable acres could eliminate about 7.4 gigatonnes of carbon dioxide by 2050 without displacing farmland. It would be more than any other route. It may seem like a lot, but 7 gigatons of carbon dioxide equals 7 billion metric tons, or less than 1 part per million by volume. The cost is estimated up to $50 per metric ton. So even with trees, the cost to remove 1 part per million volume could be as high as $390 billion.
geoengineering is also expensive.
So, for hundreds of billions of dollars, the best prospect is a small drop of 1 part per million volume in the concentration of carbon dioxide.
This arithmetic highlights the enormous need to reduce emissions. There is no viable workaround.