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Lessons about a future warmer world using data from the past - 26/06/2018

Research by a group of scientists from 17 countries has concluded that many current climate models may be underestimating projected changes within the next 80 years.

The research, published in Nature Geoscience this week, shows that climate zones will shift and ice sheets will substantially shrink over a time scale of 1000 years. 

Iceberg

The finding was an outcome of a workshop that took place in Bern, Switzerland, and was coordinated by the University of Bern, the University of New South Wales, and Oregon State University in the United States.

The compiled evidence from the past suggests that even with a global warming limited to within 2°C above preindustrial levels, as aimed at in the Paris Agreement, climate zones and ecosystems will shift, rapid polar warming may release additional greenhouse gases, and sea-level will rise by several meters over several thousand years.

These observations show that many current climate models designed to project changes within this century may underestimate longer-term changes.

One of the co-authors on the paper, Giuseppe Cortese of GNS Science, said although the study represented a great synthesis of available data, the southwest Pacific was still data-poor, making the teasing out of regional past climate scenarios difficult for our region.

“In recent years, however, many projects developed and carried out by New Zealand researchers aimed to address this shortcoming, by looking at the regional expression of multiple past warm intervals, their oceanic temperature fingerprint, and their consequences, both in terms of sea-level rise and ecosystem changes,” Dr Cortese said.

“Ultimately, we will use these patterns, as recognised in the fossil record, as a final test for climate models’ skills, which is essential to establish solid and reliable climate and environmental policies for our future.

The research concluded that ecosystems and climate zones will generally shift poleward or to higher altitudes. In response, permafrost thaw may release additional carbon dioxide and methane to the atmosphere, driving additional warming.

Past observations suggest that if warming can be limited to no more than 2°C as proposed by the Paris accords, the risk of catastrophic runaway greenhouse gas feedbacks is relatively low. Nevertheless, the significant amount of additional CO2 released from permafrost and soils must be considered in future emission budgets.

Lead author, Hubertus Fischer of the University of Bern, said accounting for the additional release of CO2 leaves even less room for error or delay as humanity seeks to lower its CO2 emissions and stabilize global climate within reasonable limits.

Even a warming of 1.5-2°C above preindustrial levels will be sufficient to trigger substantial long-term melting of ice in Greenland and Antarctica and sea-level rise of more than 6 meters that will last for thousands of years. Rates of sea-level rise higher than those of the last decades are likely.

Study contributor, Alan Mix of Oregon State University, said we are already beginning to see the effects of rising sea level. “This rise may become unstoppable for millennia, impacting much of the world’s population, infrastructure, and economic activity that is located near the shoreline.”

Another co-author, Katrin Meissner of University of New South Wales, said that “while climate model projections seem to be trustworthy when considering relatively small changes over the next decades, it is worrisome that these models likely underestimate climate change under higher emission scenarios, such as a ‘business as usual’ scenario, and especially over longer time scales.”

Detailing how these global changes play out on a smaller, regional scale, remains an important aspect of this type of research, as it provides the link to the end-users of climate-and environmental-related services and resources, including policy-makers, the public, and regional authorities.

According to the researchers, this information from the past underscores the urgency of reducing CO2 emissions soon to meet the Paris Agreements in this century and beyond.