Grade 12 Climate Change Notes PDF

**UNIT TWO** **CLIMATE CHANGE** **2.1 Basic Concepts of Climate Change** **Climate** refers to the conditions of the atmosphere in a certain place over many years. For example, the climate in Gondar is cold in the winter, and the climate in Gambella is warm and humid all year long. The climate in...

**UNIT TWO** **CLIMATE CHANGE** **2.1 Basic Concepts of Climate Change** **Climate** refers to the conditions of the atmosphere in a certain place over many years. For example, the climate in Gondar is cold in the winter, and the climate in Gambella is warm and humid all year long. The climate in one area, like the Horn of Africa, is called a **regional climate**. The average climate around the world is called **global climate**. When scientists talk about global climate change, they are talking about the global climate and a pattern of change that's happening over many years. One of the most important trends that scientists look at is the average temperature of the Earth, which has been increasing for many years. This is called **global warming.** Rising global temperatures [lead to other changes] around the world, such as [stronger hurricanes], [melting glaciers], and [the loss of wildlife habitats]. This is because the Earth's air, water, and land are all [interdependent and prone to the climate change]. This means a change in one place can lead to other changes somewhere else. For example, when air temperatures rise, the oceans absorb more heat from the atmosphere and become warmer. Warmer oceans, in turn, can cause stronger storms. According to the Intergovernmental Panel on Climate Change (IPCC), [Climate change] refers to a change in the state of the climate that can be identified by [changes in the mean and/or the variability of its properties and that persists for an extended period], typically decades or longer. It refers to any change in climate overtime, due to either natural variability or human activities. Previous assessments have already shown through multiple lines of evidence that the climate is changing across our planet, **largely as a result of human activities**. The most convincing evidence of climate change derives from observations of the atmosphere, land and oceans. A clear evidence from in situ observations and ice core records shows that the atmospheric concentrations of important green-house gases such as carbon dioxide (CO~2~), methane (CH~4~), and nitrous oxide (N~2~O) have increased over the last few centuries. **2.2 Trends in Global Change** The Earth's climate has always changed and evolved. Some of these changes have been due to natural causes, but others can be attributed to human activities such as deforestation, atmospheric emissions from industry and transport, which resulted in the storage of gases and aerosols in the atmosphere. They are known as **greenhouse gases (GHGs)** because they [trap heat and raise air temperatures near the ground,] acting like a greenhouse on the surface of the planet. The Intergovernmental Panel on Climate Change (IPCC) pointed out in its 2001 Third Assessment Report on the state of the global climate that an increasing body of observations gave a collective picture of a warming world and other changes in the climate system. The report documented that the 1990s had been the warmest decade worldwide, and 1998 the warmest year since instrumental records had begun in 1861. The report also indicated that the twentieth century was likely to have been the warmest century in the last 1,000 years. Subsquently, the observed evidences revealed that most of the warming experienced over the past 50 years had resulted from human activities. Hence, the implication suggests, human influence will continue to change atmospheric composition throughout the twenty first century. Global warming has [begun to affect] the sea level, snow cover, ice sheets and rainfall. Shifts in regional patterns of climate marked by rising air temperatures are already [affecting watersheds and ecosystems] in many parts of the world. The average global surface temperature has warmed 0.800C in the past century and 0.600C in the past three decades. The IPCC has projected that if greenhouse gas (GHG) emissions, the leading cause of climate change, continue to rise, the [mean global temperatures will increase] from 1.40C to 5.80C by the end of the 21st century (IPCC 2001). **2.3. Natural and Human Induced Climate Change**