24/02/2019 Climate Change Climate Change1 - Observations

What is Weather ? Weather is the state of the atmosphere at a place and time as regards heat, dryness, sunshine, wind, rain, etc. "if the weather's good we can go for a walk"

What is Climate Climate is the aggregated pattern of weather, meaning averages, extremes, timing, spatial distribution of… hot & cold cloudy & clear humid & dry drizzles & downpours snowfall, & snowmelt blizzards, tornadoes, & typhoons Climate change means altered patterns. Global average temperature is just one measure of the state of the global climate as expressed in these patterns. Small temperature changes  big changes in the patterns. (after Holdren NCES, 2008)

24/02/2019 What is Climate Change? Climate is the average weather at a given point and time of year, over a long period (typically 30 years). We expect the weather to change a lot from day to day, but we expect the climate to remain relatively constant. If the climate doesn’t remain constant, we call it climate change. The key question is what is a significant change – and this depends upon the underlying level of climate variability Crucial to understand difference between climate change and climate variability… Climate Change1 - Observations

Observations of climate change

Climate change Temperatures are rising rapidly, following increases in CO2 emissions and concentrations. Temperatures will rise further. Many aspects of weather have changed, and will continue to do so.

1.Temperatures have risen Global surface temperatures have risen by about 0.6°C since 1900 It is likely that this warming is larger than for any century since 200AD, and that the 1990s were the warmest decade in the last millennium.

Contd… The warming differs in different parts of the world, but over the last 25 years, almost everywhere has warmed, and very few places have cooled. 2.Sea level has risen by about 20 cm, 3.Ocean heat content has increased, 4. Almost all mountain glaciers have retreated

5.Coincident with this global warming, levels of CO2 (and other ‘greenhouse’ gases) have dramatically increased, to levels higher than those experienced for maybe millions of years.

World Health Organization 24 February 2019 Many aspects of weather have changed, and will continue to do so –IPCC= Intergovernmental Panel on Climate Change  IPCC 2007 What is climate change? 11

What causes Earth’s climate to change? Overall caused by Changes in the atmosphere 1.Natural processes Volcanoes Tectonic plate movement Changes in the sun Shifts in Earth’s orbit 2.Human activities – any activity that releases “greenhouse gases” into the atmosphere

The Role of Human Beings National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council The Role of Human Beings It is very likely that most of the climate change in the current era is the result of human activities. Human activities have increased concentrations of greenhouse gases in the atmosphere. These gases trap heat and cause the Earth to warm. See Ecological Impacts of Climate Change booklet, p. 5 Although scientific knowledge of climate is far from complete, the uncertainties concern the details: the scientific community is highly confident in the basic conclusions. The physical processes that cause climate change are scientifically well documented: both human activities and natural variability are contributing. According to the Intergovernmental Panel on Climate Change, whose documents are considered the most authoritative source for information on the “state of the science” on climate change, it is very likely that most of the observed warming over the past 50 years is the result of increased greenhouse gases generated by human activities. Numerous expert reports from the National Research Council have supported this conclusion as well. The release of greenhouse gases has increased significantly since the Industrial Revolution, mostly from the burning of fossil fuels for energy, agriculture, industrial processes, and transportation. Carbon dioxide, a major greenhouse gas, is increasing in the atmosphere faster than at any time measured in the past, having grown by about 35 percent since 1850. Two other greenhouse gases, methane and nitrous oxide, are present in the atmosphere at much lower concentrations than carbon dioxide but have increased rapidly. Methane has increased by 150 percent; in addition, it is 25 times more effective per molecule at trapping heat than carbon dioxide. Nitrous oxide, nearly 300 times more effective, has increased by more than 20 percent.

Thanks