The IPCC’s Recipe for a Livable Planet: Grow Trees, Don’t Burn Them

While most of the US spent the last few days torqued with rage over the Kavanaugh confirmation, something profoundly important for the planet was happening across the world in South Korea: the Intergovernmental Panel on Climate Change (IPCC) finalized the “Summary for Policymakers” (SPM) for the Special Report on Global Warming of 1.5°C.  The SPM distills the major messages of the longer report and offers clear guidance on what steps are needed to protect the earth from catastrophic warming.

See the SPM here.

As in prior IPCC statements, the SPM warns the “carbon budget” – the amount of cumulative CO2 that can be emitted before we irrevocably commit the atmosphere to dangerous warming – is shrinking rapidly, and drastic reductions in GHG emissions are required immediately. Yet the message and tone of the report are, if not optimistic, at least not apocalyptic (admittedly, working on climate change can move the goal posts on what constitutes “optimism”).

Throughout, the SPM compares scientific modeling of the consequences of a 1.5° C temperature rise (2.7° F) versus a 2° C rise (3.6° F).  Given the impacts of climate warming already occurring with about 1° rise, it should not be surprising that impacts will intensify. The report contains specific metrics of loss and damage, such as an estimate that 10 million more people will be impacted by sea-level rise at warming of 2° C than 1.5° C.

To halt warming, we need “net zero” emissions, in which the global system takes up as much CO2 as is emitted (additionally, we must greatly reduce emissions of non-CO2 GHG’s like methane and nitrous oxide). The SPM explains, “The maximum temperature reached is then determined by cumulative net global anthropogenic CO2 emissions up to the time of net zero CO2 emissions and the level of non-CO2 radiative forcing in the decades prior to the time that maximum temperatures are reached (medium confidence).”

Currently, global emissions are around 42 billion tonnes per year, and CO2 uptake is nowhere near that. So how do we get to net zero emissions?

The SPM features four main pathways for reducing emissions and increasing carbon storage.  Three of the four are low-overshoot/no-overshoot scenarios wherein temperature rise is constrained to around 1.5° C, and one scenario envisions temperature rise overshooting 1.5 C followed by the need for drastic drawdown of CO2, relying on “biomass energy and carbon capture and storage” (BECCS), an unproven technology with potentially damaging side-effects.  Of the three low-/no-overshoot scenarios, two also envision increased CO2 uptake using BECCS.

Only one scenario – which we’ve designated the “Green Path” – provides a realistic way forward. The first scenario is the only livable one because it limits or avoids overshoot, and it doesn’t rely on BECCS, an uproven, unscalable, and costly technology, to increase CO2 storage. The following table excerpted from the report explains the features of this green path.

Highlighted features include a rapid reduction in energy use, but not an unrealistic one: a 15% decrease in energy use compared to 2010 by 2030, and a 32% decrease by 2050. The reduction in emissions is relatively greater, due to strong increase in renewable energy. Of particular note, however, is that the pathway does not count on biomass electricity generation as renewable energy; in fact the scenario envisions a decrease in bioenergy relative to 2010.  This is because this scenario prioritizes maximizing carbon storage by forests, not burning them for energy (you don’t get to do both!).

Of course, forest restoration and afforestation – if it’s done right, using native species, not plantations – offers a host of ecosystem benefits such as clean water, habitat for plants and animals, non-wood resources, and, too often forgotten, a home for the Indigenous peoples who are still the best protectors of the last intact forest ecosystems on earth. This pathway is most compatible with the report’s emphasis on considering “ethics and equity” to help poor and disadvantaged people cope with the effects of climate change.

The SPM concludes with “high confidence” for the green path scenario that “Significant near-term emissions reductions and measures to lower energy and land demand can limit CDR deployment to a few hundred GtCO2 without reliance on bioenergy with carbon capture and storage (BECCS).” In other words, it’s probably achievable.

It turns out that old saying was right all along: trees really are the answer.