Water in the Atmosphere | Class 11 Geography Notes

Global Warming

Global warming refers to the gradual increase in Earth's average surface temperature due to the enhanced greenhouse effect caused by increased concentrations of greenhouse gases (GHGs) in the atmosphere. The atmosphere acts like a greenhouse: it transmits incoming solar radiation but absorbs most of the long-wave radiation emitted by Earth's surface, trapping heat. This is analogous to a greenhouse made of glass, which allows short-wave solar radiation in but prevents long-wave radiation from escaping, warming the interior. Similarly, closed vehicles in summer feel hotter inside due to trapped heat. Primary GHGs include carbon dioxide (CO₂), chlorofluorocarbons (CFCs), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃). Other gases like nitric oxide (NO) and carbon monoxide (CO) react with GHGs, affecting their concentrations. The effectiveness of a GHG depends on its concentration increase, atmospheric lifetime, and the wavelength of radiation it absorbs. CFCs are highly effective GHGs. Ozone absorbs ultraviolet radiation in the stratosphere but can absorb terrestrial radiation when present in the lower troposphere. The longer a GHG remains in the atmosphere, the longer it takes for the climate system to recover from its effects. CO₂ is the most abundant GHG, primarily emitted from fossil fuel combustion. Forests and oceans act as sinks for CO₂, but deforestation increases atmospheric CO₂. The atmospheric CO₂ concentration adjusts over 20-50 years and is rising about 0.5% annually. Doubling CO₂ concentration over pre-industrial levels is a key index in climate models. CFCs, products of human activity, destroy stratospheric ozone, creating the 'ozone hole,' especially over Antarctica, allowing harmful ultraviolet rays to reach Earth's surface. International efforts like the Kyoto Protocol (1997) aim to reduce GHG emissions. Global warming effects include rising sea levels due to melting glaciers and thermal expansion, threatening coastal areas and islands. The annual average near-surface air temperature of the world is approximately 14°C, with notable warming during 1901-44 and 1977-99. The seven warmest years between 1856 and 2000 occurred in the 1990s, with 1998 being the warmest year on record.

📊 Diagram: See figure_1: ice Coriunobibbles; See figure_2: In research station for the European Project for Ice Coring in Antarctica.; See figure_3: This file photo shows dead fish lying on the dried bottom of the Ding An reservoir in China's Hainan Island.; See figure_4: This image shows how the Gangotri glacier terminus has reflected since 1780.

🧪 Activity: Project Work: Collect information about Kyoto declaration related to global climate changes.

🔗 Connection: This section concludes the chapter by linking climate classification and change to contemporary environmental concerns and international responses.