Where does the heat go? A new report on the Earth Energy Imbalance by GCOS answers the question

The deployment of an Argo float into the ocean. Credit: CSRIO

The Earth Energy Imbalance (EEI), is described as the difference between the amount of energy from the sun arriving at the Earth and the amount returning to space. It serves as a fundamental metric to allow the scientific community and the public to assess how well the world responds to the task of bringing climate change under control.

According to GCOS, the new report represents the most accurate, state-of-the-art Earth heat inventory study to date.  It indicates that the Earth Energy Imbalance continues to grow unabated and has doubled in the past decade (2010-2018) compared against the 1971-2018 mean value.

Over the period 1971-2018, approximately 1% of this heat resides in the atmosphere. The vast majority of excess heat (89%) is absorbed by the ocean. New assessments of borehole measurements show that the land heating is 6%. About 4% of excess heat causes loss (melting) of both land ice and floating ice.

In this interview, we hear from lead author, Dr. Karina von Schuckmann, and Professor Han Dolman, Chair of the GCOS Steering Committee.

You, along with thirty other researchers, have been looking into Earth’s Energy Imbalance. Essentially, you’ve been looking into answering the question – where does the heat go? What have you discovered? Can you tell us a bit about the research methods you used in finding the answers?

Karina: We have been looking at the Earth heat inventory. Due to climate change, there is currently a positive Earth energy imbalance at the top of the atmosphere, meaning less heat is going out, than it is going in. We wanted to know where this heat is stored in the Earth system components, such as the ocean, the atmosphere, land and cryosphere. This was a very multidisciplinary approach – we established an international team covering the different Earth system components, the climate observation system and models to reach our findings.

Han: These are long term climate data series on essential climate variables that GCOS has identified in order to understand climate change. For the ocean observation there has been a new system used since early in the 21^st century using Argo floats, which is a really comprehensive set of data, which has reduced uncertainty in the results.

Climate deniers jump on uncertainty so this is a very strong message coming from the report.

Han: It’s hard to read the mind of a climate change denier. What the researchers were able to do with these data sets was to get the number within 10% of certainty. This is a major achievement. It’s a consistent analysis and it should be welcomed.

The report identifies that 89% of the energy coming from the greenhouse gas effect is going into the ocean.  We’re about to enter the UN Decade of Ocean Science for Sustainable Development. What do your findings mean for the ocean and indeed the planet?

Karina: The Ocean is providing a major ecosystem service for us, because it is taking up the majority of this accumulated heat from climate change in the Earth’s system. The direct impact is ocean warming which is driving a 30-40% of global mean sea level rise, that will have various consequences, especially on marine ecosystems.  And of most concern is the rapid changes that have taken place in the last decade we have observed in our study. The ocean is at risk, and the UN Decade of Ocean Science for Sustainable Development is a unique opportunity to create the Future We Want by energizing ocean science and information for future generations.

Han: In principle it looks nice that the ocean takes up all that energy, but the disadvantage is that at a particular point in time, that energy will have come out again. It is a long-term reservoir of heat, and some of its warming has an impact in certain areas, such as the glaciers.

Karina: This heat that is stored in the Earth system is in fact “heat in the pipeline” – the Earth system has not yet responded to this heat, and it has increased rapidly. Yes, the number is very high for the ocean at 89%, but even if other numbers of the heat inventory appear small, like 4% for the cryosphere, this still has major impacts for planetary system. Today, land ice melt accounts for about 70% of global mean sea level rise.

Han: Yes, the 6% going into the land has major effects on heatwaves and things like food and water security.  It’s still a considerable amount of energy.

The UNFCCC since 1992, and more recently emphasized by the Paris Climate Agreement in 2015, requires that EEI be reduced to approximately zero to restore Earth’s system towards quasi-equilibrium. Currently, the EEI indicator is around 0.87 W/m2. It sounds like a pretty daunting task – to reduce the EEI to zero, we need to reduce CO2 in the atmosphere from 410ppm to 350ppm.  How can observation systems, particularly ocean and climate observations, assist in bringing climate change under control?

Han: It would be really nice if governments and policy makers would listen to climatologists in the same way they listen to virologists during this pandemic. In practice, it’s going to be a hard task, and even more difficult to get CO2 out of the air. We should have started 10 years ago.

Karina: We could achieve so much through international transdisciplinary research based on the climate observing systems. We need to sustain and extend our observing systems. Our report notes that there are measurement gaps, and we must reduce uncertainty through improved monitoring so we can better plan for the future. We also need to see if we are achieving our goals, or whether we are reaching tipping points. We can only do this through sustained and extensive observing systems.

Han: Our ocean observing system is vulnerable. During the COVID-19 crisis, the ordinary work of replacing Argos floats was severely impacted, leading to problems in data collection.  If it is not a pandemic, there will be another crisis, or future crises – we must have a robust observing system that is also expanded to counter these extreme forces. 

Do you have a sense of hope that with a robust observing system and policymakers that listen to climatologists, science and the public can fix this?

Han: I wouldn’t be human if I didn’t have hope. The observing system is like taking the temperature of a sick planet. The observing system allows us to determine that the planet has a high fever – we know it has a high fever – but now we know beyond certainty. What we need now is the caring parents to take the sick planet to the doctor and apply the medicine. This is where the policymakers and pubic come in.

Karina: I echo what Han has said. I believe this new report is giving hope – here was a huge commitment from many experts in international teams around the world, who provided unique engagement, in order to work on this topic and make the best estimate  of the EEI and provide this information to the public. Our findings provide crucial information for the 6^th Assessment Report of the Intergovernmental Panel on Climate Change and for policymakers, particularly in the context of the UN 2030 agenda of Sustainable Development Goals.

The Global Climate Observing System (GCOS) was established following the signing on 9 April 1992 of a Memorandum of Understanding by the WMO, the IOC of UNESCO, UNEP and the ISC (Formally ICSU).

Image credit: CSIRO

Additional reporting: GCOS