Climate change includes both global warming and the resulting large scale shifts in weather patterns. There have been previous periods of climatic change but since the mid twentieth century humans have had an unprecedented impact on Earth climate system and caused change on a global scale. The largest driver of warming is the emission of gases that create a greenhouse effect of which more than ninety percentage are carbon dioxide and methane. Fossil fuel burning for energy consumption is the main source of these emissions with additional contributions from agricultural deforestation and manufacturing. The human cause of climate change is not disputed by any scientific body of national or international standing. Temperature rise is accelerating. It is tempered by climate feedbacks such as loss of sunlight reflecting snow or ice cover and increased water vapours. Changes in land and ocean carbon sinks are also a climate feedback.Temperature rise on land is about twice the global average increase leading to desert expansion and more common heat waves plus wildfires. Temperature rise is also amplified in the Arctic where it has contributed to melting permafrost glacial retreat and sea ice loss.Warmer temperatures are increasing rates of evaporation causing more intense storms and weather extremes. Impacts on ecosystems include the relocation or extinction of many species as their environment changes most immediately in coral reefs mountains and the Arctic. Climate change threatens people with various problems such as food insecurity or water scarcity and flooding along with infectious diseases and extreme heat waves. These human impacts have led the World Health Organization to call climate change the greatest threat to global health in the twenty first century. Even if efforts to minimise future warming are successful some effects will continue for centuries including rising sea levels and ocean temperatures. The Intergovernmental Panel on Climate Change has issued a series of reports that project significant increases in these impacts as warming continues at a rapid rate. Further additional warming also increases the risk of triggering critical thresholds called tipping points. Responding to these impacts involves both mitigation and adaptation. Mitigation or limiting climate change consists of reducing greenhouse gas emissions and removing them from the atmosphere. Methods to achieve this include the development and deployment of low carbon energy sources such as wind and solar energy and a phase out of coal enhanced energy. Forest preservation is another important aspect of mitigation. Adaptation consists of adjusting to actual or expected climate such as through improved coastline protection and better disaster management along with assisted colonisation and the development of more resistant crops. Adaptation alone cannot avert the risk of severe widespread and irreversible impacts. The environmental effects of climate change are broad and far reaching. Changes may occur gradually or rapidly.Evidence for these effects comes from studying climate change in the past and from modern observation. Since the droughts and heatwaves have appeared simultaneously with increasing frequency. Extremely wet or dry events within the monsoon period have increased in India and East Asia. The rainfall rate and intensity of hurricanes and typhoons is likely increasing. Frequency of tropical cyclones ha snot increased as a result of climate change. Global sea level is rising as a consequence of glacial melt and melt of the ice sheets in Greenland and Antarctica.