Weather refers to the exact state of the atmosphere at a particular location and time. Climate refers to the long-term patterns or statistics of the weather.

Climate change describes the long-term differences in the statistics of weather patterns measured over multi-decadal periods. Climate change is also sometimes referred to as global warming. However, in its most literal meaning, global warming only refers to increasing temperatures, while climate change also includes changes in all other aspects of the climate (e.g., precipitation, sea level, land use).

The warming is not uniform—land warmed more than the ocean and the northern hemisphere warmed more than the tropics or the southern hemisphere. This is important because about 85% of the world’s population lives on land in the northern hemisphere, meaning that they have experienced more warming over the past 150 years than the global average warming.

We have an adequate observational history of the last 150 years covering enough of the planet that we can measure climate change over that period. The surface thermometer record shows that the Earth has warmed by 1.1°C over this time (calculated as the difference between the 1850–1900 average and the 2009–2018 average). As of early 2021, the warmest year in the record was 2016 fol-lowed by 2020, 2019, 2017, and 2015.

About 93% of the heat trapped by greenhouse gases goes into heating the oceans. The heat content of the top 2 km/1.25 miles of the ocean, and it shows that the oceans are gaining energy. There are two key contributing factors to the rise in sea level. One contributor is the melting of grounded ice. When it melts and the water runs into the ocean, the total amount of water in the ocean increases and sea level rises. Second, water, like most things, expands when it warms. The oceans are indeed heating, and the resulting thermal expansion should also raise sea level. These two processes have contributed about equally to sea level rise over the past century.