Short answer
Warming beyond biome temperature limits cuts how much carbon land plants take up. In “How close are we to the temperature tipping point of the terrestrial biosphere?” (Science Advances, 2021), Katharyn Duffy and colleagues find the terrestrial biosphere’s temperature tipping point lies within the next 20 to 30 years. Without mitigating warming, the most productive biomes cross their thresholds by midcentury, after which the land carbon sink could degrade to only about 50% of current capacity if adaptation does not occur.
Warming and terrestrial net primary productivity
Science Advances work on temperature tipping risks for the terrestrial biosphere, including rainforests and taiga that cycle large shares of land carbon, underpins this post.
Why it matters: weaker land sinks amplify climate change even if fossil emissions hold steady.
Follow the linked analysis on temperature thresholds and productivity loss timing. The takeaway is that biosphere feedbacks can front-load damage this century.
How close are we to the temperature tipping point of the terrestrial biosphere? | Science Advances
However, the impact of elevated temperatures on the land sink is more than a function of cumulative area. Biomes that cycle 40 to 70% of all terrestrial carbon (19) including the rainforests of the Amazon and Southeast Asia and the Taiga forests of Russia and Canada are some of the first to exceed biome-specific TmaxP�Pmax for half the year or more. This reduction in land sink strength is effectively front-loaded in that a 45% loss occurs by midcentury, with only an additional 5% loss by the end of the century (Fig. 3D). Furthermore, these estimates are conservative as they assume full recovery of vegetation after temperature stress and ignore patterns and lags in recovery (25).
Basically, as net positive climate forcings increase, we will continue to decrease net carbon capture by the terrestrial ecosystems of the earth as a whole. (LS)
The temperature tipping point of the terrestrial biosphere lies not at the end of the century or beyond, but within the next 20 to 30 years (Figs. 2 and 3, A to D). Given the temperature limits of land carbon uptake presented here, without mitigating warming, we will cross the temperature threshold of the most productive biomes by midcentury, after which the land sink will degrade to only ~50% of current capacity if adaptation does not occur. While biomes will eventually shift spatially in response to warming, this process is unlikely to be a smooth migration, but rather a rapid disturbance-driven loss of present biomes (with additional emissions of carbon to the atmosphere), followed by a slower establishment of biomes more suited to the emerging climate. Furthermore, the establishment of new biomes is unlikely to be complete without human intervention and will be limited by edaphic factors, especially nutrient availability. This further suggests that we are rapidly entering temperature regimes where biosphere productivity will precipitously decline and calls into question the future viability of the land sink, along with Intended Nationally Determined Contributions (INDCs) within the Paris Climate Accord, as these rely heavily on land uptake of carbon to meet pledges (33)
Frequently asked questions
How does global warming affect net primary productivity?
As temperatures pass biome-specific limits, land carbon uptake declines. A 2021 Science Advances study by Duffy and colleagues finds that, without mitigating warming, the most productive biomes cross their temperature thresholds by midcentury, after which the land sink could fall to about 50% of current capacity if adaptation does not occur.
Which ecosystems are affected first?
Biomes that cycle 40 to 70% of all terrestrial carbon, including the rainforests of the Amazon and Southeast Asia and the taiga forests of Russia and Canada, are among the first to exceed their biome-specific temperature limits for half the year or more.
When will most of the loss in land carbon uptake happen?
The loss is front-loaded: the study estimates a 45% loss in land sink strength by midcentury, with only an additional 5% by the end of the century. The authors call these estimates conservative because they assume full recovery of vegetation after temperature stress.
Why does this matter for the Paris Agreement?
National pledges under the Paris Climate Accord rely heavily on land uptake of carbon, so a declining land sink calls their viability into question.