Equilibrium Climate Sensitivity (ECS) refers to the increase in global average surface temperature that would occur if the concentration of carbon dioxide (CO₂) in the atmosphere were to double. This measurement reflects the anticipated temperature rise after the climate system has reached a state of equilibrium, which may take centuries or even millennia. At this point, the deep ocean will have fully responded to the changes, and all feedback processes will have been accounted for.
At the current atmospheric concentration of 429.42 parts per million (ppm) of CO2, we are 77% of the way towards doubling the pre-industrial level of 280 ppm. Since the pre-industrial level was 245 ppm, at the current rate, 1000 years (50 generations) from now, the atmospheric concentration will be 1143 ppm, which would be a quadrupling of the pre-industrial level.
As the following NOAA graphic demonstrates, the rate of emissions has increased exponentially since about 1960 and at the current temperatures will rise in accordance with Michael Mann’s hockey stick.
According to the IPCC’s Sixth Assessment Report of 2021, based on instrumental observations, paleoclimate evidence, and climate modelling, the likely temperature ranges for a doubling of CO2 are estimated to be 2.5°C to 4°C. With a best estimate of ~3°C.
Since ECS is a property of the climate system that depends on the amount of CO2 we emit, the surface temperature could rise by 6°C as a result of the ECS. While this figure is not likely to change significantly over time, the actual warming after 1,000 years will depend on how much CO2 is emitted and for how long the atmospheric concentration remains elevated.
ECS is a concept defined by meteorologist Jule Charney in the 1979 report titled "Carbon Dioxide and Climate: A Scientific Assessment," commissioned by the National Academy of Sciences. It refers to the fast climate feedback mechanisms, including water vapor, clouds, and aerosols.
In contrast to the ECS, the Earth System Sensitivity (ESS) encompasses all feedbacks, including slow feedbacks like ice sheet melting, permafrost melting, which releases methane into the atmosphere, and changes in the carbon cycle, which doubles the ECS.
The timescale to full realization of the ECS is ~100-200 years, and for the ESS, it is 500- 1000+ years, and at the upper range, this will be 50 generations from now.
Mark Lynas' book "Six Degrees of Climate Emergency" refers to six degrees as the "doomsday scenario" because it envisions dramatic changes like the transformation of the oceans into marine wastelands, extensive desertification, and a significant increase in the frequency and severity of extreme weather events.
James Hansen and his colleagues' research indicates that the equilibrium global warming potential for today's greenhouse gas levels is 10°C, which is reduced to 8°C by today's human-made aerosols.
Aerosols reflect sunlight into space, and their removal would allow more solar radiation to reach the Earth's surface. So, our offspring could be confronted by the conundrum of clear skies at 10 °C, or 8°C plus respiratory and cardiovascular disease, lung cancer, diabetes, neurological disorders, and adverse pregnancy outcomes associated with burning fossil fuels.
On our current course, 50 generations from now, our offspring, or whatever is left of them, will be doomed to marine wastelands, extensive desertification, extreme weather, and a damaged, uninhabitable planet.
The actionable steps we can take to reverse this course are:
1. Advocate for policies that facilitate the transition to renewable energy, support conservation efforts to protect natural habitats, implement sustainable agricultural practices, and invest in climate change research and development.
2. Promote peace, foster inclusive governance, uphold human rights, promote social justice and equality, and uphold the rule of law.
3. While short-term economic gains can be appealing, politicians must ensure long-term financial viability and avoid unsustainable practices that deplete resources or create instability. In the alternative, they need to invest in education and the development of human capital and diversify their economies to reduce reliance on vulnerable sectors.
4. Our duty of care includes leaving a legacy of ethical leadership and responsible decision-making: transparency, accountability, and a commitment to a standard of good governance.
There is a widely held belief that politicians' primary responsibility is to their current constituents and that predicting the needs of future generations is not part of their role. This perspective often prioritizes short-term economic growth, even at the expense of long-term environmental consequences. While this viewpoint is ubiquitous, it doesn’t diminish the ethical obligation to consider the well-being of future generations.
Intergenerational justice is the concept that each generation has a moral obligation to ensure that future generations have the same, or even better, opportunities and resources as they did. It emphasizes fairness across time, extending beyond just a single generation.
The actions or inactions of current generations should not unfairly disadvantage future generations. This includes avoiding environmental damage, unsustainable resource depletion, and debt accumulation.
Current generations are responsible for leaving behind a world that is environmentally and socially sustainable, capable of meeting future generations' needs.
Given the chance, the grandchildren you love will have grandchildren of their own whom they will love as much as you love them, and so on, times 17. So, we need to act accordingly.
The best way to do that is to provide them with the cheapest available, zero-emission energy that mitigates every consequence of climate change.