Earth's Energy Imbalance and Global Warming Solutions
Alongside the massive expansion (and funding) of land restoration and regenerative agriculture schemes and the reduction of CO2, are other solutions on the horizon?
Introduction
This post explores this week's Planetary Health Check and the long-term Earth Energy Imbalance. Alongside the massive expansion (and funding) of land restoration and regenerative agriculture schemes and the reduction of CO2, are other solutions on the horizon?
The Planetary Health Check
Earlier this week we saw the launch of the Planetary Health Check report, a remarkable piece of interdisciplinary science research.
The report, to be released annually, is essentially an update on the PIK Planetary Boundaries framework. Unsurprisingly, the report does make for some rather grim reading:
“… the patient, Planet Earth, is in critical condition. Six of nine Planetary Boundaries are transgressed. Seven PB processes show a trend of increasing pressure so that we will soon see the majority of the Planetary Health Check parameters in the high-risk zone” ???
Johan Rockstr?m
But the report comes with a clear message – this is “science for change”
“local actions impact the planet, and a planet under pressure can impact everyone, everywhere. Securing human wellbeing, economic development, and stable societies requires a holistic approach where the protection of the planet takes center stage”????
Levke Caesar, PIK, Co-Lead of PBScience
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The messaging of continued damage to the biosphere amidst inadequate action is clear:
?"We have the technology and knowledge to solve the climate crisis; we just need the political will." James Hansen
The solutions to?limit and reverse?the ecological crisis (including climate change) are already known. For greater detail please also refer to my recent posts on the subject here and here.
Summarising:
In the short-term, what is needed is to coordinate with developing nations to oversee a massive expansion (and funding) of land restoration and regenerative agriculture schemes. If done quickly, this can provide the necessary mitigation action required.
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The Earth System and The Earth’s Energy Budget
The Earth System
The Earth system is composed of the natural spheres (the hydrosphere, biosphere, atmosphere, cryosphere and geosphere) – all interconnected and open – through which we can observe fluxes of energy, mass and momentum. Viewing the Earth in isolation - as a closed system - these fluxes eventually cycle through, so that outputs re-enter the system to become inputs, creating feedbacks and feedback chains. Each subsystem ultimately affects the response of every other subsystem and of the climate as a whole.
The Earth’s climate system displays nonlinearity - inputs and outputs are not proportional. Looking at the historical climate record, change is often episodic and abrupt. The occurrence of more nonlinear effects and risks in recent times highlights a climate system driven by climate forcings and human system feedback effects.
The Earth’s Energy Budget
"We cannot negotiate with the laws of physics. We must adapt to a changing climate."
James Hansen
Global warming?occurs over?the entire globe – its ocean layers, atmospheric layers, land and ice surfaces. We tend to focus on only one metric - global mean surface temperature – which for better or worse over-simplifies matters. The Paris goal of 1.5 C, and the various long-term forecasts warning of breaching 2 C, 3 C and so on. All of this relative to a pre-industrial average temperature benchmark. Looking at the Earth’s Energy budget provides greater depth.
The Earth’s energy budget defines the prospects for continued global warming and climate. A budget surplus of energy is the determinant of excess heat, leading to increased surface temperatures, and increased temperatures above and below the surface.
As with any budget, it has natural variability. Small changes in?heat transfer?from the ocean to the?atmosphere, or vice versa,?can create significant changes in?surface temperature. Similarly, changes in greenhouse gases (GHGs) will affect the climate forcings at a higher level, increasing the surplus energy.
We use the term climate forcing, or radiative forcing (RF) to describe the various positive and negative factors that contribute to Earth’s overall energy budget. These factors are called forcings because they drive the climate to change. They are also external forcings, because they exist and operate independently of the climate system. Examples include variations in solar radiation, volcanic eruptions, changing albedo, and changing levels of GHGs in the atmosphere.
On the left hand side of the above budget are the GHGs, which have the effect of trapping radiation that would otherwise go back into space, and are positive climate forcings. CO2 has the largest effect, but one can see that methane (CH4) is also significant and increasing.
On the right hand side of the budget, we have atmospheric aerosol concentrations and outgoing radiation, which are negative climate forcings that act to cool the planet. Note that the outgoing radiation is also increasing steadily, showing that the planet is becoming increasingly hot and therefore radiating more energy back into space.
Historical increases in the GHG concentrations are responsible?for positive climate forcing, causing a gain of energy in the climate system. In contrast,?changes in atmospheric aerosol concentrations result in a negative climate forcing leading to a loss of energy.
It is the balance between these various climate forcings that drive the change in global energy. A net positive climate forcing means a budget surplus of energy. The excess energy has to go somewhere, of course, and most of it goes into the oceans.
Net Flux and Earth’s Energy Imbalance (EEI)
In a steady climate the Earth receives as much energy from the Sun as it sends back into space. Some of the solar energy is reflected by e.g. clouds and small particles (aerosols), some is absorbed by GHGs e.g. carbon dioxide, ozone and water vapour, and some is reflected or absorbed by Earth's surface.
Earth's net radiation, also called net flux or net TOA flux, is the balance between the incoming and outgoing energy at the top of the atmosphere. It is the total energy available to influence the climate.
When we look at the entire planet's?energy budget over time, we see that the planet has been steadily accumulating?heat?since the 1970s, due to positive net flux.
Does the Sun play a major role in this?
The short answer is no.
The Energy Imbalance has developed over a period of around 55 years i.e. 5 solar cycles.
During strong solar cycles, the Sun's total average brightness varies by up to 1 W/m2, typically affecting global average temperature by 0.1 C or less. Therefore projected warming from increasing GHG levels will more than offset even a very strong Grand Solar Minimum.
How the excess energy is transferred
As above, the Earth system is composed of the natural spheres (the hydrosphere, biosphere atmosphere, cryosphere and geosphere) – all interconnected and open – through which we can observe fluxes of energy, mass and momentum.
From a physics perspective, the excess energy is variously transferred into four states:
There is a complex interplay and system of feedbacks between these various states.
Scientists model the climate’s response to the excess energy using a climate response function. Per James Hansen, this shows how much of the excess energy is still “in the pipeline”, to be introduced over the long term. The response function has a characteristic shape, achieving almost half of its equilibrium response quickly, within about a decade. The remaining response (to 90%) is largely complete after 100 years, with a very long tail.
Where the excess energy is distributed
Results obtained in a recent paper (K. von Schuckmann et al, 2023) reveal a total Earth system heat gain of 381 ± 61 ZJ over the period 1971–2020,
with an associated total heating rate of 0.48 ± 0.1 W/m2. About 89% of this heat was stored in the ocean, about 6% on land, 4% in the cryosphere, and 1% in the atmosphere.
The most recent period shows a higher heating rate of 0.76 ± 0.2 W/m2 over the period 2006-2020.
For this period 2006-2020, about 89% was stored in the ocean, 5% on land, 4% in the cryosphere, and 2% in the atmosphere.
The primary reasons for these distributions of excess heat relate to the heat capacity of the various climate system components, the specific heat of water versus land versus air, and the masses involved (Trenberth 2022).
See also Appendix 2 for a more detailed look at how the excess heat manifests in the oceans, atmosphere, cryosphere and on land.
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EEI Measurements
The Excess Energy has historically been estimated from an inventory of the changes in energy, with complex workings involved. When combined with net TOA flux measurements (directly measured by satellites), it enables us to better understand the changes in EEI over time.?
See also Appendix 1 for a look at the components of net TOA flux.
Taking another recent paper, we have an even higher heating estimate,
EEI = 0.90 ± 0.15 W/m2 for the period 2005 – 2019.
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Measures for EEI can now be tracked online at the following link , with the latest EEI (based on June 2024 data) measure shown as 0.95 W/m2.
Reducing the EEI - Global Warming Solutions
The EEI is arguably the most important measure related to climate change.
It is the net balance caused by all the processes and feedbacks, positive and negative, that are in play in the climate system.
Taking an Earth surface area of 509.5 million km2 and multiplying, this gives the global energy equivalent, total global EEI = 0.95 x 509.5 = 484 TW.
To put this into perspective, this energy imbalance is almost 80 times current annual global electricity generation (at 6.06 TW). And steadily increasing.
Reducing the Energy Imbalance
To bring the Earth back towards energy balance, and ignoring other potential solutions, this would mean the amount of CO2 in the atmosphere reducing from the current 423 ppm average down to around 350 ppm.
"Climate change is not about politics, it's about survival."
James Hansen
But there are other methods we can also use. The reduction of this colossal amount of excess energy necessitates a reduction in incoming radiation absorbed, and an increase in outgoing radiation, which in broad terms means:
These solutions are also to some degree, interconnected. For example restoring natural capital has a knock-on effect on evapotranspiration and water transport, which implies more cloud cover, water vapour and so on. As per usual, doing "all of the above" is probably the best approach given how little time remains.
Climate interventions
A side note on climate interventions and "geoengineering" solutions and funding, as these will be increasingly on the radar.
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?Appendix 1 - The Components of EEI and Net Flux
Net TOA flux is the balance of the various components of radiation at TOA (top-of-the-atmosphere), namely the absorbed solar radiation (ASR) and the net outgoing longwave radiation (OLR). The net flux or net radiation, is the ASR minus OLR.
The ASR is the net incoming (short wave) radiation absorbed, after allowing for reflected radiation. It varies with forcings and feedbacks - from clouds, water vapour (WV), aerosols (SFC, AER) etc - which all have their own distributions and variability around the globe at any time.
The OLR is the net outgoing (long wave) radiation emitted to space, also known as emitted terrestrial radiation. The OLR plays an important role in planetary cooling. The OLR is radiation in the infrared part of the spectrum, as opposed to the near-infrared radiation found in sunlight. Less than 1% of sunlight has wavelengths greater than 4 μm, whereas 99% of longwave radiation has wavelengths in the range 4-100 μm.
Net Flux varies with latitude in particular, but also longitude.
Maps for net flux and its components can be found online here.
The net TOA flux measure tells us how much excess energy is in the system and, given the climate response is not immediate, how much more energy budget is “in the pipeline”, which will affect the planet over time.
?Appendix 2 - Energy Imbalance - Effects on the Earth
Climate change is the corollary from the transfer of the excess energy - direct and indirect heating of the oceans, land, cryosphere and atmosphere.
This affects levels and potentials of temperature, cloud cover, water vapour, albedo, salinity and other physical factors, in a complex interplay of planetary processes.
Feedback effects are another outcome of increased warming, leading to non-linearities in the climate system. These may be physical (e.g. ice sheet-albedo interaction), biogeophysical (e.g. albedo-vegetation interaction), or biogeochemical (eg. GHG-atmosphere interaction) in nature.
Warming Oceans
There is a progressive warming of the oceans at the surface layer, and with a time lag – the deeper layers of the oceans. Surface ocean warming has been observed since 1980, with warming of deeper layers noted in 1990 (500-1000m), 1998 (1000-1500m) and 2005 (1500-2000m).? Warming and natural variability create hot spots, sometimes called 'marine heat waves', that vary from year to year but are increasing. Other hot spots eventually result in more atmospheric activity, leading to hurricanes which serve to remove heat from the ocean. All five oceans are warming, with the largest amounts of warming in the Atlantic Ocean and Southern Ocean surrounding Antarctica.
Warming Atmosphere
Climate change is typically seen in terms of the lowest regions of the atmosphere – warming surface temperatures and frequent record temperatures worldwide. There is also a lot more natural variability in surface air temperatures than in ocean temperatures because of El Ni?o/La Ni?a and weather events.
Paradoxically, while the atmosphere close to the Earth’s surface (troposphere) is warming, the atmosphere above (stratosphere) is becoming colder.
The same GHGs that trap and slow radiation in the bottom few miles of the atmosphere, lead to cooling of the atmospheric layers higher up.?
Warming Cryosphere
The cryosphere and Earth system interact through atmospheric circulation, precipitation, water levels and mountain range erosion. As part of the global climate system, snow and ice cool the planet by reflecting solar energy from their white surface back into space (the albedo effect). Through convection, conduction and feedback processes, increased snow and ice melt caused by temperature increases, leads to lower albedo, further warming and further melting (ice-albedo feedback). Changing water composition from meltwater affects ocean circulation. Moisture transfers from the cryosphere influence cloud cover formation, precipitation and atmospheric circulation. These feedbacks influence long-term trends in climate and regional weather patterns.?
Warming Land
The impacts of climate change on terrestrial natural ecosystems are already prevalent, such as land degradation, desertification, permafrost degradation and food insecurity.
As temperatures warm, the percentage of drylands (45%) is expected to increase, putting further pressures on land resources, ecosystem services and biodiversity. Air temperatures over land have increased faster than the global average and are about 1.5°C warmer compared to the pre-industrial era. This is nearly double the rate of increase in global average temperature i.e. including the oceans.
Land plays a key role in the exchange of energy, water and aerosols between the land surface and atmosphere. The terrestrial biosphere absorbs almost 30% of anthropogenic CO2?emissions. This vital function is under attack, with increased droughts and wildfires, deforestation and other environmental and human pressures. Climate change increases ongoing land degradation through increased heavy precipitation and increased heat stress.?Land use changes further affect the energy and water balance, leading to further local effects on temperature and precipitation.
Anthropogenic emissions from deforestation currently outweigh the benefits from afforestation and reforestation. Agriculture is responsible for about 50% of anthropogenic methane emissions and is the main source of nitrous oxide emissions.
Future global warming will further aggravate the degradation processes through floods, more frequent droughts, stronger cyclones, and sea level rise. This will adversely affect agricultural production in many regions.