The worst-case climate-change scenario could look like this. We need to avert it

Sometimes you need to confront the worst possible outcome in order to avert it.

The raging wildfires and Atomic tangerine skies that have recently plagued the western US are yet another example of the impact of climate change. And, they may be a mere prelude to more disturbing developments on the horizon.

Experts attempting to rank the severity of climate change scenarios likely to play out by the year 2100 refer to the worst of them as “RCP 8.5.” There are several of these “Representative Concentration Pathways” starting with the best-case scenario, RCP 1.9 – where warming above pre-industrial levels is limited to about 1.5°C, alongside steep declines in emissions.

The World Economic Forum has used data from the Climate Impact Lab, Climate Central, the Washington Post, and NASA satellites to create a visualization* of this worst-case scenario that helps illustrate some projected impacts.

Below is an excerpt showing the worst-case view of temperature change around the world through the end of this century, where average temperatures from June through August over the years are represented by a dark blue equal to 0°C (32°F) and below, which becomes progressively warmer in shades of light blue, green, yellow, orange, and a dark red equal to 38°C (100.4°F) and above.

Phoenix, Arizona is already well known for its heat. Last month, the city – with an expanding population of 1.7 million people relying on air conditioning – broke a 46-year-old record by registering its eighth day of the year with temperatures of at least 115°F (46.1°C).

Conditions may get even more uncomfortable for America’s hottest city. In the worst-case scenario visualization excerpt below, the number of days in Phoenix per year that hit at least 32°C may reach 199 by 2100 – compared with an average of 158 days per year during the 20th century.

On the other side of the US, Florida is faced with increasing temperatures and rising sea levels. In the excerpt below we see projections for the unhindered disappearance of Florida coastline if temperatures are allowed to increase by 4°C above pre-industrial levels.

While seawalls and levees can be built to protect much of Florida’s coastline, some communities there have found the cost to be prohibitive. According to one estimate, it would collectively cost Florida nearly $76 billion – an amount equal to the bulk of the state’s current annual budget – to build the seawalls necessary to stave off rising sea levels by 2040.

South Asia would be hit hard under the worst-case climate scenario, and the most vulnerable people there would likely disproportionately absorb the impact. The worst-case scenario would see people fleeing from the impacts of climate change account for nearly a quarter of all internal migrants in the region by 2050.

The dark red in the excerpt below represents average temperatures from June through August equal to 38°C (100.4°F) and above. New Delhi, a city of about 22 million people where air conditioning already accounts for more than half of all summertime electricity use, could go from about six months per year averaging 32°C as of 1960 to eight months by 2100.

The ASEAN region is also likely to be heavily impacted in this worst-case scenario. In the excerpt below, orange represents average temperatures from June through August in excess of 30°C (86°F). The region is already one of the most vulnerable to the extreme weather and rising sea levels associated with global warming.

In Viet Nam, significant portions of the country are projected to be subsumed by rising sea levels by 2050, while in Bangladesh more than 13 million people could be displaced by the various impacts of climate change by that same year.

Europe, where at least 22 million farmers and agricultural workers are exposed to climate extremes, is also likely to see dramatic change by the year 2100 if this worst-case climate scenario plays out.

In the excerpt below, we can see average temperatures from June through August in southern Spain, Italy and Greece reaching roughly 30°C (86°F). In addition to warming, climate change can also affect precipitation patterns. In London, maximum annual temperatures may be 4°C hotter on average by the 2070s – when the city may also see an additional 52 millimetres in average annual precipitation.

It is a bleak forecast, but the worst impacts of climate change can be avoided if major polluting nations implement effective climate policies. We also limit warming by fighting efforts to discredit legitimate science, removing carbon dioxide from the atmosphere or offsetting it by planting new forests, and upgrading transportation and energy systems.

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*Projections represent average annual temperatures under high emissions (RCP 8.5) with a median probability. Climate Impact Lab's method captures the full range uncertainty around how the climate will respond to increased GHG concentrations. It created a temperature distribution representing a range of equilibrium climate sensitivity from 1.5°C to 5.9°C (an ECS based on evidence in IPCC’s most recent synthesis assessment, AR5) to analyze what might happen in low-probability, high-risk futures (.95 & .05). 17-83% is the “likely range” for IPCC and most climate estimates, which is why the authors chose to visualize the median probability.