Lecture 03 - Climate Change PDF

Climate Variability Climate variability refers to variations in the mean state and other statistics (such as the occurrence of extremes, etc.) of the climate on all temporal and spatial scales beyond that of individual weather events. Variability may be due to natural internal processes w...

Climate Variability Climate variability refers to variations in the mean state and other statistics (such as the occurrence of extremes, etc.) of the climate on all temporal and spatial scales beyond that of individual weather events. Variability may be due to natural internal processes within the climate system (internal variability), or to variations in natural or anthropogenic external forcing (external variability). 2 What is climate change? Climate change is a change in the pattern of weather, and related changes in oceans, land surfaces and ice sheets, that have come to define Earth’s local, regional and global climates and occurring over time scales of decades or longer. 3 Energy Balance The temperature of the Earth is determined by a balance of the energy entering the Earth–atmosphere system and the energy leaving the system. Global energy balance (GEB): Earth's stored energy = Energy the earth receives from the Sun - Energy the earth releases to space. 4 The greenhouse effect Greenhouse gases in the atmosphere, including water vapour, carbon dioxide, methane, and nitrous oxide, absorb heat energy and emit it in all directions (including downwards), keeping Earth’s surface and lower atmosphere warm. Adding more greenhouse gases to the atmosphere enhances the effect, making Earth’s surface and lower atmosphere even warmer. 5 Climate Forcing Any process or activity that influences the GEP either by increasing or decreasing the earth’s stored energy contributes to climate change and is qualified to be called a climate forcing process. Climate forcing as an imbalance in energy at the top of the Earth's atmosphere either externally or by human activities. 6 Climate Forcing Climate forcing processes are classified as: Internal Climate Forcing Processes - processes operating on the GEB from within the earth. External Climate Forcing Processes - processes operating on the GEB from outside the earth. 7 Climate Change The internal and external climate forcing processes except the man-made processes are grouped together as natural causes of climate change. You can edit this text You can edit this text Natural cause Climate Earth Change Anthropogenic causes Global temperature 8 External Climate Forcing Processes 1- Variations in the amount of energy received from the sun. 2- Variations in the earth’s orbit around the sun. 9 Internal Climate Forcing Processes 1. Oceans 2. Continental Drift 3. Atmosphere 4. Water Cycle 5. Clouds 6. Ice and Snow 7. Land Surfaces 8. Volcanic Eruptions 9. Human Causes 10 Internal Climate Forcing Processes 1. Oceans Oceans are the key source of moisture in the air through interactions with the atmosphere. Oceans also store heat efficiently, transporting it thousands of miles thus redistributing heat in time and space. The oceans and marine life also consume huge amounts of carbon dioxide. These ocean-based processes exert tremendous influence on global climate and accounts for the variations. 11 Internal Climate Forcing Processes 2. Continental Drift Scientists believe that the our earth is still slowly drifting and constantly changing. This constant drifting is believe to have impact on the climate because it changes the physical features of the landmass, their position and the position of water bodies. The separation of the landmasses changed the flow of ocean currents and winds, which affects the climate. 12 Internal Climate Forcing Processes 3. Atmosphere The atmosphere stores a lot of heat or energy which comes from the sun. This energy regulates the earth's climate. The atmosphere composes of small particles and several gases out of which are the green house gases (GHGs) that store heat. The small particles (aerosols) tend to block sunlight reaching the earth. 4. Water Cycle Higher air temperatures can increase water evaporation and melting of ice. Water vapour is the most potent greenhouse gas. Clouds also affect evaporation, creating a cooling effect. 13 Internal Climate Forcing Processes 5. Clouds Clouds reflect solar energy (cooling the earth) and thereby trapping heat being radiated up from the surface (warming the earth). Clouds variability contribute to climate change. 6. Ice and Snow The whiteness of ice and snow reflects heat out, cooling the planet. When ice melts into the sea, this drives heat from the ocean causing variability in climate. 14 Internal Climate Forcing Processes 7. Land Surfaces Mountain ranges can block clouds, creating "dry" shadows downwind. Sloping land allows more water runoff, leaving the land and air drier. A tropical forest will soak up carbon dioxide, but once cleared for cattle ranching, the same land becomes a source of methane, a greenhouse gas. 8. Volcanic Eruptions A volcanic eruption emits large volumes of sulphur dioxide (SO2), water vapour, dust, and ash into the atmosphere that influence climatic patterns for years. The gases and dust particles partially block the incoming rays of the sun, leading to cooling. 15 Evidence of Climate Change Observations show that the global average sea level has risen by about 16 cm since the late 19th century. Sea level is rising faster in recent decades; measurements from tide gauges (blue) and satellites (red) indicate that the best estimate for the average sea level rise over the last decade is centred on 3.6 mm per year. The shaded area represents the sea level uncertainty, which has decreased as the number of gauge sites used in calculating the global averages and the number of data points have increased 22 Consequences of climate change Changes in Glaciers and ice sheets Sea level change Sea ice Heavy rainfall across the globe Extreme Drought Decline in Crop productivity Changes in ecosystems Hurricanes Rise in temperature Acidification of seawater 27