To limit planetary warming to 1.5° Celsius (C), we need to undertake an immediate, multi-trillion-dollar transformation of global energy, land-use, food production, transportation, and urban systems, stated the Intergovernmental Panel on Climate Change (IPCC) in a new report that aggregates the findings of thousands of scientific studies. Humanity can only put a maximum of 420 more gigatons of greenhouse gas emissions into the atmosphere if we want a good chance of only increasing temperatures by 1.5° C (2.7° Fahrenheit), instead of 2° C (3.6° Fahrenheit). At the current pace, our remaining carbon budget will be used up by 2030. The transformation that has already begun in many parts of the world must accelerate and scale across the globe.
To date, global temperatures have increased 1° C (1.8° F) above pre-industrial levels. The IPCC argues that limiting warming to just another half a degree Celsius will still have terrible global impacts, but stave off some of the worst effects and make a major difference for several hundred million people.
Achieving the 1.5° C limit can only happen in the very near term. IPCC states if the planet can achieve net-zero emissions in the coming decades that would essentially halt warming. But if emissions reductions instead occur at a much slower pace up until 2100, then planetary feedback loops — like defrosting permafrost perpetuating warming trends — would make halting warming at 1.5° C impossible.
There are significant differences between 1.5° C and 2° C increases. A 1.5° C temperature increase would mean about 4 inches less of sea level rise by 2100, and at a much slower rate of rise. This would buy time to help the hundreds of million of people who live on coasts and deltas to adapt their infrastructure with resilient natural systems that can also restore and bolster important coastal habitats.
With a 1.5° C increase, some 6 percent of insects, 8 percent of plants, and 4 percent of vertebrates are projected to “lose over half of the climatically-determined geographic range” — meaning their habitat will disappear. While this is awful, the scenario at 2° C increase is far worse: 18 percent of insects, 16 percent of plants, and 8 percent of vertebrates. Impacts from forest fires and invasive species would also be commensurably more at 2° C.
The chance of an ice-free Arctic Ocean during summer is far less with a 1.5° C scenario. But coral reefs face a dire future under both 1.5° C and 2° C scenarios: either a 70-90 percent loss with 1.5° C or near-total extinction with 2° C.
Climate change is also expected to have major impacts on food production, resulting in reduced yields and less nutritious crops. Limiting warming to just 1.5° C would result in “smaller reductions in yields of maize, rice, wheat, and other cereal crops, particularly in Sub-Saharan Africa, Southeast Asia, and Center and South America.” The report authors are also semi-confident that limiting warming to 1.5° C would also reduce the populations affected by water shortages by 50 percent. Still, millions of people would be impacted.
The IPCC report outlines potential pathways to zero carbon. Essentially, greenhouse gas emissions must drop by 45 percent by 2030 and 100 percent by 2050. This would require “rapid and far-reaching transitions in energy, land, urban, and infrastructure (including transport and buildings), and industrial systems.”
IPCC admit that the changes are unprecedented in terms of scale — but not speed. Previous economic and social transformations have occurred with a few years; think of the US economic transformation during World War II or the appearance of smartphone apps in 2007 and their widespread application today.
The report estimates the damage of a 1.5° C increase to the global economy to be tens of trillions a year as soon as 2040. To avoid this, major investments must be made. The report calls for investing $2.4 trillion a year on renewable energy through 2035, which would be about 2.5 percent of global GDP annually, while weaning off coal. The planet would also need another 10 million square kilometers in forests, taken back from agricultural land, and a dramatic reduction in emissions from buildings and transportation systems through energy efficiency and smart growth.
A recent analysis conducted as part of Drawdown, a publication that ranks the 80 most effective ways to reduce greenhouse gas emissions, yielded solutions where landscape architects and planners can help accelerate the transformation. These include: afforestation (#15); mass transit (#37); water savings at home (#46); restoring and protecting coastal wetlands (#52); walkable cities (#54); bike infrastructure (#59); and green roofs (#73). There are also some landscape architects involved in siting renewable energy infrastructure, restoring farm land, managing forests and peatlands, which all rank highly.
IPCC is confident this global transformation can occur. If a mix of adaptation and mitigation measures can be “implemented in a participatory and integrated manner,” they can enable a “rapid systemic transition.” Adaptation measures don’t have to be purely defensive — they can also help communities improve, ensuring “food and water security, reducing disaster risks, improving health conditions, maintaining ecosystem services, and reducing poverty and inequality.” Now, the political will is needed to act.
Read about the recommendations of the ASLA Blue Ribbon Panel on Climate Change and Resilience, which span adaptation and mitigation, and explore ASLA’s guides to climate change mitigation and resilient design.