A decade ago, scientists believed that unchecked global warming could heat the world to 1.5 degrees C (2.7 degrees F) above preindustrial levels sometime around 2045. It now looks like we could pass this critical threshold as soon as 2030. Indeed, some research points to up to 3 degrees C (5.4 degrees F) of warming by 2050.
The difference in numbers here may sound small, but the implications are huge. Every fraction of a degree of warming above 1.5 degrees C will bring new weather extremes to many places — heat waves, fires, floods and more — alongside devastating impacts on lives and livelihoods.
While climate treaties and their negotiators trade in the language of degrees, it can be hard to relate global temperatures to what people are likely to experience in a particular locale — or how governments can prepare for these impacts.
To help fill in the picture, we analyzed dozens of climate models to discover how 1.5 and 3 degrees C of global warming might affect approximately 1,000 of the world’s largest cities. We focused on a few key impacts that many cities will face as temperatures rise:
- Extreme heat directly impacts health, productivity and economies, and is especially severe in cities due to urban heat island effect. We looked at the average number of heat waves cities could experience per year, as well as the average duration of each year’s longest heat wave.
- Energy demand for cooling has implications for power grids, electricity costs and greenhouse gas emissions. We looked at the number of cooling degree-days cities could face at each temperature threshold.
- Disease risk; specifically, how many days per year cities could experience temperatures conducive to the spread of insect-borne diseases, including arboviruses and malaria.
So, what do the models show where you live?
How Rising Temperatures Could Affect Your City
Choose a city below, and you will see five visualizations — one for each of the climate hazards we studied. Each chart compares the hazard at 1.5 and 3 degrees C of warming based on three separate climate models. Because different models usually produce different estimates, we present them as ranges rather than single numbers. The wider the ranges, the more the models disagree with each other. They commonly agree on the direction, if not the magnitude, of change.
A few notes of caution. Climate models cannot offer perfect predictions due to scientific uncertainty, technical limitations and the fact that weather is always somewhat unpredictable. Our models are also built on global climate simulations which do not consider many local details, such as buildings and landforms. Because buildings and pavement are not well represented, the models tend to underestimate urban heat island effect and therefore temperatures.
Because of the uncertainties involved, these modeling results should also not be seen as predictions, but as general trends for these cities as the world warms.
These Impacts Aren’t Inevitable
These models underscore how much every fraction of a degree matters. As the planet warms, we will feel the impacts ratcheting up — damaging economies, hurting our health, and making cities, which are home to more than half of humanity, less livable.
Responding to the impacts that are already here is critical. Governments can do much to protect communities by investing in cooling infrastructure and data-driven climate-resilient planning. WRI recently launched the Cool Cities Lab, a data visualization and scenario-testing tool supporting cities in their responses to extreme heat.
But it’s important to remember that how much global warming the world experiences is driven by human systems.
Some countries have ramped up their commitments to limit greenhouse gas emissions, and climate action worldwide has already made the most unimaginably hot futures much less likely. It’s still within our power to stop well short of 3 degrees C and avoid much of the damage we’re likely to see if we carry on with business as usual. It will require greater ambition and stronger commitment to act, and it must happen right away — but we can still secure a safer, more livable future.
