*5.1.1 Temperature*

Temperature records from modern thermometers (with temperature scales) have been available only since early 18th century. By studying indirect parameters (chemical and structural signatures), scientists can infer past temperatures.

At the creation of the universe, the temperature of the universe at 10−35 second old was around 1 octillion°C. Within less than 2 minutes, the universe temperature cooled down to around 1 billion°C. Over at least the last several million years, planet Earth shifted between ice ages facing long cold periods (glacial) and warm periods (interglacial), on 100,000-year cycles.

The current climate change is associated with increased Earth's temperature (land surfaces and upper layers of the ocean) (**Figure 2**) [1, 4]. Land surfaces are heating faster than ocean surfaces. A warmer atmosphere can hold more water vapor, leading to increased overall average precipitation [4]. Over the past 70 years, the Earth's temperature has increased by approximately 0.7°C [4]. Since 1950, the number of cold days and nights has decreased while the number of warm days and nights has increased. Since 1976, the rate of warming has been greater than at any other time during the last 1,000 years. For any given period, there are extreme temperatures. In the past 20 years, Earth's lowest air temperature was −94.7°C (recorded in Antarctica in 2010) and hottest air temperature was 70.7°C (recorded in Iran's Lut Desert in 2005). The present global mean temperature is around 15.0°C. Currently, the surface temperatures are rising by approximately 0.2°C per decade [6]. According to the Intergovernmental Panel on Climate Change (IPCC) and based on different emissions scenarios, there will be a rise in global mean temperatures of 0.9 to 5.4°C by 2100 [4].

#### **Figure 2.**

*Climate change is associated with increased Earth's temperature.*

The rise in global mean temperature is not the same everywhere. There are regional variations in Earth's temperature. Some areas will not even get warmer and may actually get cooler in the short term [4]. Warming is more pronounced at higher latitudes. The North Pole and Northern Hemisphere have warmed much faster than the South Pole and Southern Hemisphere. Greater temperature increases are expected in winter compared to summer and in nighttime versus daytime. Springs occur earlier and winters are milder.
