Exploring the drivers of modern global warming
Global surface temperatures have risen around 1.3C since the preindustrial (1850-1900) period as a result of human activity. 1 However, this aggregate number masks a lot of underlying factors that contribute to global surface temperature changes over time.
These include CO2, which is the primary driver of long-term warming, as well as non-CO2 greenhouse gases like CH4, N2O, and halocarbons. But it also includes planet-cooling aerosols that have masked a sizable portion of the warming of our greenhouse gas emissions to-date. Rounding out the list are other anthropogenic factors (tropospheric ozone, albedo changes due to land use change), and natural forcings (primarily volcanic eruptions and variations in solar output).
To disentangle the respective contributions of each of these requires a climate model. Here I will be using the latest version of FaIR, a reduced complexity climate model that has been used extensively by the community for assessing global-level changes. The implementation of FaIR used here is specifically designed to reproduce both observed climate change since pre-industrial and assessed climate metrics from the IPCC Sixth Assessment Report (AR6). This approach has the advantage of providing robust uncertainties that reflect the range of relevant parameters (e.g. climate sensitivity, carbon cycle feedback strength, ocean heat uptake rates, etc.) in-line with the ranges in the AR6.
However, unlike the climate simulations featured in the AR6, which only use climate forcings based on real-world observations through 2014 and explore different scenarios (SSPs) thereafter, these simulations use observationally-informed forcing estimate through the end of 2023 from Forster et al 2024. This has the advantage of allowing us to explore how actual changes in real-world emissions (e.g. including factors like rapid Chinese aerosol declines and low-sulfur shipping rules) have impacted global temperatures.
