University of California Santa Cruz

Global climate has been changing throughout the entire 4.5 billion years of Earth’s history and global sea level closely reflects those climate changes. When the planet gets warmer, seawater warms and expands, and ice melts. Both of these processes affect global sea level, which rose about 125 meters following the end of the last Ice Age about 20,000 years ago. The period from 1901-2016 is the warmest in the history of modern civilization and based on extensive evidence, it is extremely likely that human activities, especially greenhouse gas emissions, are the dominant cause of this warming. The rate of global sea-level rise has increased in response and is highly likely to continue to increase in the decades ahead. While natural coastal environments have been adjusting to large fluctuations in sea level over millions of years, our global civilization and large coastal cities have never had to adjust to a rise in sea level. With approximately 150 million people around the world today living within a meter of high tide, the future rise in sea level may be the greatest challenge that human civilization has ever faced.