The 2-degree-Celsius temperature rise limit globally accepted as a means to avoid dangerous climate change is a "mathematical aggregate" and a mere average of data collected from hundreds of climate stations around the world and thrown into climate models to forecast the effects of climate change. It fails to protect those nations most at risk, according to Petra Tschakert, a professor at Pennsylvania State University and coordinating lead author of the Intergovernmental Panel on Climate Change's Fifth Assessment Report.

For many countries, especially African nations, small island states and developing nations, adopting a temperature rise target of 1.5 C would potentially be safer, Tschakert wrote.

Writing in the journal Climate Change Responses, Tschakert said more than 70 percent of parties negotiating at climate talks in Lima, Peru, last December repeatedly warned that a 2 C increase in temperature would place their communities at great risk.

"Two degrees is an aggregate. No real person, plant or coral reef experiences a mathematical average on a daily basis," she said. "They experience unevenness, extreme events, shifts in trends that are more subtle. This is how climate change looks like in real life."

The problem lies in the interpretation of what consists of dangerous climate change and a community's ability to adapt, Tschakert said, the latter being something vulnerable populations may not have the resources to do.


Tschakert participated in the fourth structured expert dialogue at Lima, the most recent event in the two-year review process of the 2 C limit. When parties to the U.N. Framework Convention on Climate Change accepted the long-term global goal to reduce greenhouse gas emissions in order to hold the increase in global average temperature below 2 C, they also decided to periodically review the adequacy of this goal and overall progress being made toward achieving the goal. The review is also considering strengthening the long-term global goal, including in relation to temperature rises of 1.5 C.

The process began in 2013, and the results are expected in June.

Experts exposed the costs and benefits of limiting warming to a given level and consequences of delayed action on how it affects things like food security and health around the world. Tschakert spoke on the ways in which climate change would impact livelihoods, migration and conflict.

A 2 C limit, which is disproportionately supported by wealthy countries, does not take into consideration how the impacts of climate change, extreme weather and warming already are threatening -- and will continue to threaten -- disadvantaged populations, such as people living in the megacities of Lagos, Nigeria, or Shanghai, she said.

Battle for 1.5 degrees

The push for a 1.5 C global temperature limit has been going on for a while. Many nations, and increasingly religious organizations, have expressed support for the lower limit.

During the Lima negotiations, nine Catholic bishops from five countries called for delegates in Paris "to adopt a fair and legally binding global agreement based on the universal human rights applicable to all." They said such an agreement should keep global temperature rise below 1.5 C. On Monday, the Global Catholic Climate Movement released a petition asking for the same reduced limit.

Patrick Carolan, executive director of the Franciscan Action Network and one of the founders of the movement, said one reason the group is calling for a lower limit is that warming above that level is expected to jeopardize many people's way of life. He pointed to the islands of Micronesia, with a population of about 104,000, most of whom live near the coast and survive by subsistence fishing.

The islands are threatened by rising sea levels three times the global average, about 0.4 inch per year. In addition, Micronesia is expected to experience increasing air and ocean surface temperatures, higher rainfall, and more intense typhoons, according to the Pacific Climate Change Science Program.

"Several of those islands are uninhabitable and people have been living on those islands for thousands of years. Whole cultures have had to change their whole ways of life to deal with what's happening," he said. "People who least contribute to climate change are the ones most affected by it, and as Catholics we have to reach out and be cognizant of that and be helpful to those who are most affected, the poorest."

Earlier this month, ministers and delegates from 54 African nations issued the Cairo Declaration, which stressed Africa's vulnerability to the effects of climate change, in particular the adverse effects on ecosystems, food production, and social and economic development. The declaration said the upcoming Paris agreement needs to ensure that the mitigation efforts must keep global temperatures below 1.5 C.

Current climate change projections for Africa suggest sea levels rising faster than the global average, 31 inches by the end of the century. Citizens in Mozambique, Tanzania, Egypt, Senegal and Morocco are all at risk of flooding. Agriculture, food security, health and water availability will be severely impacted.

Can we even prevent 2 degrees of warming?

But Granger Morgan, a professor in the department of engineering and public policy at Carnegie Mellon University, said to forget 1.5 C and, judging by the action taken thus far to make meaningful emissions reductions, forget 2 C, too.

"Two degrees would be wonderful if there was some plausible likelihood we could achieve it," he said.

Morgan said targets are useful to help quantify the "increasingly draconian things that will keep happening as we increase emissions and temperatures," but he doesn't think bringing 195 nations to a negotiating table will be the way the world gets serious about climate change. Rather, the major players and biggest emitters will need to make big commitments and stick to them, he said.

In November, the U.N. Environment Programme released a report showing the world is not on track to stave off the worst effects of climate change (ClimateWire, Nov. 20, 2014). The report lays out the milestones for meeting the 2 C goal. The world needs to cut its emissions by 15 percent below 2010 levels by 2030; by 2050, emissions need to be 55 percent of 2010 levels; and by 2080, it has to drop to zero. Renewable energy needs to be a much bigger part of the picture, the report said.

Tschakert said despite her own doubts about the ability of international climate negotiations to solve climate change, she said the 2 C limit -- which was created in the 1970s by economist William Nordhaus as a cost-benefit analysis to emissions reductions and not climate change risks and has faced repeated criticism -- is not only socially unjust for the lower-income countries, but will cost privileged countries more in the long run.

"I hope that people take away a sense of responsibility and understanding this is not just a scientific matter, not just about a bunch of countries unable to agree," she said. "It is our ethical responsibility to take care of people who cannot protect themselves. It's especially our responsibility because we have to a large extent caused the precarious situations in which these people find themselves."