Global mean warming is proportional to the total amount of CO2 emitted. This emergent property of the climate system, known as the transient climate response to cumulative CO2 emissions (TCRE) provides the basis for the concept of carbon budgets for meeting different temperature target levels, such as the 1.5 °C target. Most of the CO2 emission pathways that reach the 1.5 °C and 2.0 °C temperature stabilisation level in the long term are based on the assumption that emitting CO2 and removing it later by the implementation of artificial carbon dioxide removal from the atmosphere (CDR) leads to the same state of the climate system. However, a question remains whether the state of carbon cycle differs among scenarios in which a given temperature level is achieved without overshoot or scenarios where that temperature level is temporarily exceeded and then resorted by CDR. 

Remaining carbon budgets are also subject to different sources of uncertainty, such as the uncertainty in Earth System response to non-CO2 forcing, future non-CO2 scenario uncertainty, and uncertainties due to additional Earth System feedbacks currently under-represented in the Earth System models.

In this talk, I will discuss carbon cycle responses to idealised overshoot scenarios and their implications on TCRE and carbon budgets. I will also present an integrated approach to quantification of uncertainties in the remaining carbon budgets (both geophysical and socio-economic), using observationally-constrained quantities. Finally, I will explain the implications for the remaining carbon budget estimates in the light of the overall uncertainty, while emphasising that despite those uncertainties, the implications remain the same: we need to reach net-zero emissions to stop warming.

Short bio: 

Kasia Tokarska is a postdoctoral researcher at ETH Zurich in Reto Knutti's climate physics group, exploring climate-carbon interactions and how they change under anthropogenic influence. Her recent work focuses on estimates of the remaining carbon budgets for the Paris Agreement target and quantifying associated uncertainties. 

Kasia holds a PhD from the University of Victoria in Canada, where she worked with climate models of different complexity, exploring various aspects of the carbon budgets framework. She also researched the role of negative emissions (artificial carbon dioxide removal from the atmosphere) in the reversibility of the Earth System, and detection and attribution of anthropogenic climate change from the observed record.

Slides can be downloaded from https://www.dropbox.com/s/uur85c9fqbpn8tp/kasia_seminar.pdf?dl=1