The world has an ultimate objective to avoid dangerous interference with the climate system. Prior pages cover some climate system basics and forums to engage for learning, responding and innovating solutions. What's missing? What's still needed? We need to quantify a target and put date on it. As with anything, this can generate focus and energy among diverse individuals and groups to move quickly toward an outcome that is widely seen as desirable and important.
For climate change, world institutions, UNFCCC member states in particular, have indicated strong support for a measurable target (avoid 2°C) and a date (now and forever). On the other side of the coin, the temperature trajectory is powerful and will exceed 2°C if sufficient changes in human activities are not implemented soon enough.
Here, 'Stabilization Step 5' takes a step back to introduce the 'avoid 2°C' target, other temperature targets and some other types of targets. Whether or not 'avoid 2°C' maintains the wide support it has now, it may help to move forward with eyes wide open. Further, multiple targets may be complementary and useful.
CO2 persists in the atmosphere for periods of time that exceed multiple human lifetimes. Researchers point out that achieving guardrail temperature targets of avoiding 2°C depends on total cumulative CO2 emissions, not the path to stabilization.
This provides a scientific basis for an international policy framework to formulate targets based on total allowable greenhouse gas emissions (Zickfeld et al., 2009).
cumulative CO2 emissions over time
--some for hundreds of years and some for millennia.
A carbon budget is a one-time deal. It reflects a choice to cap the amount of carbon that will be used before we stop using carbon altogether. This is not a financial budget that renews every fiscal year
Meinshausen et al. (2009). Greenhouse-gas emission targets for limiting global
warming to 2C. Nature, 458 1158-1163.
Zickfeld, K., Eby, M., Matthews, H. D., Weaver, A. J., & Schellnhuber, H. J. (2009). Setting cumulative emissions targets to reduce the risk of dangerous climate change. Proceedings of the National Academy of Sciences of the United States of America, 106(38), 16129-16134.