How are Climate Timelines Measured?

How do we quantify the risk horizon to inform capital allocation and policy decisions?

The Mayans used sun calendars to predict the date of calamity. Economists try to predict how inflation will rise and fall.

Now, organizations try to predict when temperatures will rise above the allotted levels. They seemingly all have different dates to surpass the Paris Agreement targets.

How is the impact of climate change calculated? How do researchers form these estimates?

The Fundamentals of Climate Change

Everybody is seemingly talking about climate change. But what does this refer to, and which metrics are relevant?

Climate change refers to a long-term shift in global weather patterns and temperatures. It is primarily driven by human activity since the Industrial Revolution, when humans started rapidly burning fossil fuels.

It is a balance of incoming solar radiation from the sun and outgoing heat. There are certain gases, known as greenhouse gases, that naturally absorb heat from the sun. Some of these gases include water vapor, carbon dioxide, methane, and nitrous oxide. Without these gases trapping heat, the Earth’s average temperature would be 0°F!

Fossil fuels are items like coal, oil, and natural gas. Each of these is created by compressing fossils over thousands or millions of years. Since they are formed from organic matter, they are mostly made from carbon.

When humans burn them to create energy, they release this carbon dioxide into the air, which was previously buried in the ground as part of a natural process.

The increase of greenhouse gases in the air thickens the thermal blanket around the Earth. This traps more heat, which throws the balance of energy from the sun being reflected back out into space.

The result is the global temperature rising. Since the 1850s, the Earth’s average surface temperature has risen by 1.2 °C.

Quantifying the Risk Horizon

When sudden climate change occurs, it leads to disastrous events. So far, the rising temperatures have caused sea level rise, extreme weather events, droughts, and ecological disruption.

Ice melts from glaciers, which adds water to the ocean. The ocean absorbs large portions of carbon in the air, leading to ocean acidification and making it uninhabitable for certain species of coral reefs, and increased water vapor disrupts weather patterns.

That is why scientists try to predict how much climate change will impact the planet. These methods form an integrated toolkit.

The first tool is the Equilibrium Climate Sensitivity calculation.

Imagine that the Earth is a pot on the stove. The stove is the sun’s heat, and the pot is our atmosphere.

If we turn up the stove’s heat by adding carbon dioxide, and then we wait for a very long time for the pot to reach a new, stable temperature, how hot will it be?

This is what the Equilibrium Climate Sensitivity measures. It doesn’t tell us how long it will take to get there, but it explains how hot the planet will eventually become based on our current jump of carbon dioxide in the atmosphere. This is used to evaluate long-term risks to infrastructure like coastal real estate or nuclear power plants.

Then, researchers can use the Transient Climate Response. If we slowly turn up the stove’s heat over a few minutes, how hot will the water be after exactly one minute? This calculates the temperature at a specific point in time. This is helpful to create mid-term risk assessments for specific years, such as evaluating the impact of climate on crops in 2050.

Limitations to Calculating Risk

Like many groups predicting the future, the measurements are imprecise. This is because so much variation occurs. When scientists conduct these calculations, they have to build small-scale models to emulate the entire world.

However, some factors shift over time. One of the largest components that makes calculations imprecise is clouds.

Low-altitude clouds reflect incoming solar radiation to space. This creates a cooling effect and explains why it is chilly when it is foggy outside. High-altitude clouds trap outgoing radiation, which has a warming effect. Think of thick clouds when it is humid outside.

Right now, there are many debates about how to measure these impacts. Will warming cause more low-altitude clouds, which cool the planet? Or will it cause fewer clouds and more high-altitude clouds, which warm the planet?

Other factors that change over time are how melting glaciers and increased water vapor will change weather patterns.

A Concrete Timeframe for Action

Based on the data researchers find, there is an almost linear relationship between the Earth’s warming and the total amount of carbon we have emitted into the atmosphere. It even has its own term: Transient Climate Response to Cumulative Emissions.

This is a ratio that quantifies the amount of global temperature increase per unit of carbon emitted. The Intergovernmental Panel on Climate Change (IPCC) estimates that this value is likely in the range of 1.4 °C to 2.2 °C per 1000 gigatons of carbon.

This means that using the previous equations, we can determine approximately when we will hit certain temperature values based on our current actions.

It means that to limit global warming to a specific temperature target, like 2°C, we need to limit our total cumulative emissions. This is the basis for a carbon budget. The more we emit, the less of the budget we have left.

Right now, humans are emitting around 50 gigatons of carbon per year. The remaining carbon budget is 1150 gigatons to stay below 2°C. At our current rate of emissions, this will be exhausted in about 28 years.

However, this is not a final countdown or a definite timeline. It depends on human action. Immediate, rapid, and large-scale reductions in greenhouse gas emissions are needed to slow down this process.