Climate Science

2015 the hottest year on record – what does that mean for us?

“… temperatures will likely reach around 1.05℃ above pre-industrial temperatures. Of this, about 1℃ can be attributed to the release of greenhouse gases into the atmosphere, about 0.05ºC-0.1ºC to El Niño, and about 0.02ºC to higher solar activity. The numbers don’t quite add up to 1.05℃ due to uncertainties and natural variability.” on 2015-temperatures

In 2015, measurements from the Mauna Loa Observatory in Hawaii have shown a CO2 concentration in the atmosphere of over 400 parts per million for the first time since they started with their observations, and likely for the first time in 2.5 million years. At the same time, 2015 will probably be the hottest year on record. The reason for the high temperature is mainly our impact on the climate system (read why we know that in our previous article).

CO2 concentrations and temperatures are expected to continue to rise in the future. The Data Journalist calculated and illustrated what that means for us:

The good news is: We can do something to prevent the negative effects of climate change.

”Greenhouse gas emissions, which are causing climate change, can be controlled. We have the knowledge and the tools to act. We have a choice. Future generations will not.”
WMO Secretary-General Michel Jarraud, WMO


Data and Methods:

To obtain the number of people affected by hot temperatures, we used two data sources: The CMIP5 archive for temperature simulations and the GGI database for projections of global, gridded population. We used 15 simulations under historical forcing and 15 simulations for future temperatures under RCP8.5. Under this scenario, the radiative forcing will be 8.5 W/m2 in 2100.

We averaged monthly temperatures to yearly values. We then defined the hottest year over 1950-2010 for every grid cell on the land-surface of the globe. The temperature during that hottest year is defined as ‘hot temperature’. We then determined the year in the future after which every single year is projected to be hotter than the hottest year of the past – called ‘year of emergence’. We then simply added the number of people living in the grid-cells during the year of emergence to find the number of people affected by hot temperatures.




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