Emissions – the ‘business as usual’ story is misleading

Abstract

Heading in here running to two lines Names Name, Names Names Intro running about 8 lines across just one column Intro running about 8 lines across just one column Intro running about 8 lines across just one column Intro running about 8 lines across just one column Emissions-the 'business as usual' story is misleading Zeke Hausfather & Glen P. Peters Stop using the worst-case scenario for climate warming as the most likely outcomemore-realistic baselines make for better policy. Falling costs for generating clean electricity have led to a proliferation of wind farms, such as this one near Palm Springs, California.

ESD Reviews: mechanisms, evidence, and impacts of climate tipping elements

“…Polling of expert researchers produces a wide range of global mean temperature increases relative to pre-industrial temperature (3-4°C) for intensifying boreal forest transitions (Kriegler et al, 2009). Many 780 modeling studies to date have focused heavily on worst-case emissions scenarios like RCP8.5 (Gauthier et al, 2015;Shuman et al, 2015), which may no longer represent most-likely climate trajectories (Hausfather and Peters, 2020). Comparisons of vegetation shifts under multiple climate scenarios suggest that boreal forest changes may be strongly mitigation-dependent, with more limited impacts for more moderate emissions pathways (Lucht et al, 2006).…”

“…(Lenton et al, 2019) additionally invoke the possibility of triggering stratocumulus cloud deck evaporation (Section 2.7) as a potentially important tipping point. However, the level of greenhouse gas forcing required to cause marine stratocumulus cloud formations to break down lies at around 1200 ppm CO2 (Schneider et al, 2019), at the upper end of even aggressive, worst-1020 case emissions pathways (Hausfather and Peters, 2020).…”

“…1110 A substantial mitigating consideration, however, is that the greenhouse gas concentrations required to initiate stratocumulus cloud deck evaporation (~1200 ppm CO2 equivalent) are high, at the upper limit of potential greenhouse gas concentrations in 2100 under the very-high RCP8.5 emissions scenario. With the RCP8.5 pathway itself representing a "worst-case" emission scenario that is unlikely to be realized (Hausfather and Peters, 2020), it appears uncertain that the concentration thresholds 1115 required to trigger the stratocumulus cloud deck phenomenon will be reached this century. Thresholds for other tipping elements such as ice sheet collapse or Amazon forest dieback could be reached first at much lower levels of forcing, suggesting that the bulk of scientific and policy attention should remain on more proximate climate feedbacks.…”

Visualizations of Projected Rainfall Change in the United Kingdom: An Interview Study about User Perceptions

“…Visualizations and associated captions were presented on their own without the main text, because recommendations in the communication literature state that figures and captions should be understandable without having to read the main text [36]. We tested prototypes, so that any issues identified in the interviews could potentially be addressed in the version to be used in Met Office communications They thus still included terminology such as "business-as-usual" for describing high-emission scenarios, which was criticized recently by other authors [37]. We chose to present visualizations about projected precipitation, because precipitation in particular is expected to become more extreme in the UK, and is central to planning by UK practitioners and policy makers [7].…”

“…Participants pointed out that for the presented climate projection visualizations, the accompanying captions differed in language used for describing the same elements (such as "business-as-usual" used interchangeably with "RCP 8.5"). Furthermore, terminology may have been confusing because it included vague or outdated terms, such as "business-as-usual", for describing high-end emission scenarios [37]. We thus recommend using the same terminology in the climate projection visualizations and accompanying captions, and to ensure that terminology is clear (strategy 7).…”