Geological records stretching back millions of years indicate a number of large variations in Earth’s past climate. These have been caused by many natural factors, including changes in the sun, volcanoes, Earth’s orbit and CO2 levels.
However, comprehensive assessment by scientists shows that it is extremely likely that human activity has been the dominant cause of warming since the mid-20th Century.
Decreases density because gases have less density than liquids
If it takes ten minutes to travel 5 km, then it'll take 60 minutes to travel thirty, making your biking speed 30 kilometers per hour. 25 minutes divided by ten is 2.5. multiply 5 by 2.5 to get 12.5, your average walking speed.
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