- Climate sensitivity is usually described as the increase in global temperature when the concentration of CO2 in the atmosphere doubles from pre-industrial levels.
- Before industrialization, CO2 was around 260 parts per million (ppm), so doubling would be at approximately 520 ppm.
- Presently, atmospheric CO2 has surpassed 400 ppm, and we anticipate reaching the 520 ppm threshold in the next 50-100 years based on future greenhouse gas emissions.
There are different ways to define climate sensitivity based on the timescales under consideration. Two key measures include:
- Transient Climate Response (TCR):
- Definition: TCR is the temperature increase at the moment when atmospheric CO2 has doubled, assuming an annual increase of 1%.
- Significance: It provides insights into what we might expect over the current century, especially as atmospheric CO2 concentrations are actively changing during this period.
- Equilibrium Climate Sensitivity (ECS):
- Definition: ECS represents the temperature increase that occurs over an extended period (hundreds or even thousands of years) after the TCR point, allowing the climate system to fully adjust to a sustained doubling of CO2.
- Significance: While TCR focuses on shorter timescales, ECS considers the long-term warming potential of the climate system. However, ECS may be less directly relevant to policy decisions regarding climate change due to its extended timescales.
HOW TO ESTIMATE CLIMATE SENSITIVITY
Estimating climate sensitivity involves relying on indirect methods, as direct measurement is not possible. Three main approaches are used for estimation:
Historical Climate Records:
- Method: Analyzing instrumental records of warming since the mid-19th century, coupled with assessments of greenhouse gas and aerosol emissions.
- Application: This approach helps evaluate the global temperature response to human-induced CO2 emissions up to the present.
Climate Models:
- Method: Utilizing climate models, sophisticated simulations of Earth’s climate system, to project future climate sensitivity.
- Application: Since future climate observations are unavailable, these models provide predictions based on our understanding of the underlying physics governing the climate system.
Palaeoclimate Records:
- Method: Examining records such as ice cores to estimate natural temperature and atmospheric CO2 variations over thousands of years.
- Application: This method allows for estimates of the historical relationship between temperature and CO2 levels, providing insights into natural climate sensitivity changes.
FAQs – CLIMATE SENSITIVITY AND FEEDBACK DRIVE UNCERTAINTY
1. What is climate sensitivity?
- Climate sensitivity refers to the increase in global temperature when the concentration of CO2 in the atmosphere doubles from pre-industrial levels, typically measured in degrees Celsius.
2. What was the pre-industrial CO2 concentration, and when is it expected to double?
- Pre-industrial CO2 was around 260 parts per million (ppm). Doubling would occur at approximately 520 ppm. With current levels exceeding 400 ppm, it is anticipated to reach 520 ppm in the next 50-100 years based on greenhouse gas emissions.
3. What are the key measures of climate sensitivity?
- Two main measures are:
- Transient Climate Response (TCR): The temperature increase when CO2 doubles, assuming a 1% annual increase.
- Equilibrium Climate Sensitivity (ECS): The long-term temperature increase after the TCR point, occurring over hundreds or thousands of years.
4. Why is TCR significant?
- TCR provides insights into temperature changes over the current century, aligning with actively changing atmospheric CO2 concentrations during this period.
5. What is the significance of ECS?
- ECS considers the extended period for the climate system to fully adjust to sustained doubled CO2 levels, offering insights into long-term warming potential. However, it may be less directly relevant to short-term policy decisions.
6. How is climate sensitivity estimated?
- Estimation involves three main approaches:
- Historical Climate Records: Analyzing instrumental records of warming, combined with greenhouse gas and aerosol assessments.
- Climate Models: Utilizing simulations of Earth’s climate system for future predictions.
- Palaeoclimate Records: Examining natural temperature and CO2 variations over thousands of years from records like ice cores.
7. Why can’t climate sensitivity be directly measured?
- Direct measurement is impractical, so indirect methods combining historical records, climate models, and palaeoclimate data are employed for estimation.
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