8.1 Basics of Climate Change and Global Warming
A clear grasp of fundamental concepts is essential to navigate the complexities of climate science and policy. Let's define key terms and explore the Earth's climate system.
Weather
Refers to the short-term atmospheric conditions at a specific place and time. It includes elements like temperature, humidity, precipitation, wind, cloud cover, and atmospheric pressure. Weather is what you experience daily and can change rapidly.
Climate
Describes the long-term average weather patterns (typically over 30 years or more) that characterize a particular region. It includes average temperatures, precipitation patterns, seasonality, and the frequency of extreme weather events. Climate represents the overall state of the climate system.
Defining Climate Change
General Definition
A long-term, significant change in the "average weather" (or climate) that a given region experiences. This can manifest as changes in average temperature, precipitation, wind patterns, or the frequency of extreme weather events.
UNFCCC Definition
Article 1 of the UNFCCC defines climate change as: "a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods." This specifically emphasizes anthropogenic (human-caused) climate change.
IPCC Definition
The IPCC uses a broader definition that includes changes due to both natural variability and human activity. However, its reports overwhelmingly conclude that the current warming trend is unequivocally due to human influence.
Defining Global Warming
Global Warming Explained
Refers specifically to the ongoing increase in Earth's average surface temperature (both land and oceans) observed since the pre-industrial period (around 1850-1900). It is one of the most prominent indicators and aspects of broader climate change, primarily driven by the enhanced greenhouse effect from human activities.
Relationship with Climate Change: Global warming is a key component of climate change. The warming planet drives changes in other climate variables (e.g., precipitation, sea levels). "Climate change" is a more encompassing term.
The Earth's Climate System
The Earth's climate is a complex, interactive system consisting of five major components that exchange energy and matter:
Atmosphere
Gaseous envelope surrounding Earth.
Hydrosphere
All liquid water (oceans, lakes, rivers).
Cryosphere
All frozen water (ice sheets, glaciers).
Lithosphere
Solid Earth (continents, ocean floor).
Biosphere
All living organisms on Earth.
The Greenhouse Effect: Natural vs. Enhanced
Natural Greenhouse Effect
A vital natural process warming Earth's surface. Solar radiation warms the Earth, which then emits infrared radiation. GHGs (H₂O, CO₂, CH₄, N₂O, O₃) trap some of this heat, keeping Earth ~33°C warmer than it would be otherwise, essential for life (avg. ~15°C vs. -18°C).
Enhanced Greenhouse Effect (Anthropogenic)
Human activities (since Industrial Revolution) significantly increased atmospheric GHGs (especially CO₂, CH₄, N₂O). This traps more infrared radiation, leading to additional warming of Earth's surface and lower atmosphere – what we call global warming.
Major Greenhouse Gases (GHGs) and their Characteristics
Understanding the properties of different GHGs is crucial. Global Warming Potential (GWP) measures heat-trapping ability relative to CO₂ over 100 years.
| Greenhouse Gas | Formula | Anthropogenic Sources | Atmospheric Lifetime | GWP (100-yr) |
|---|---|---|---|---|
| Carbon Dioxide | CO₂ | Fossil fuels, deforestation, cement | Variable (50-200+ yrs) | 1 |
| Methane | CH₄ | Agriculture, natural gas leaks, landfills | ~12 years | 28-36 |
| Nitrous Oxide | N₂O | Agriculture (fertilizers), industry, fossil fuels | ~114 years | 265-298 |
| Fluorinated Gases (F-gases) - Entirely Anthropogenic | ||||
| Hydrofluorocarbons (HFCs) | Various | Refrigerants, AC, aerosols | Variable (yrs to decades) | 100s to 10,000s |
| Perfluorocarbons (PFCs) | Various | Aluminum, semiconductor mfg. | 1,000s of years | 1,000s to 10,000s |
| Sulfur Hexafluoride (SF₆) | SF₆ | Electrical transmission, magnesium prod. | ~3,200 years | ~23,500 |
| Nitrogen Trifluoride (NF₃) | NF₃ | Flat-panel displays, solar cells | ~740 years | ~17,200 |
| Other Important Gases | ||||
| Tropospheric Ozone | O₃ | Photochemical reactions (NOx, VOCs) | Short (hours-days) | Variable (indirect) |
| Water Vapor | H₂O | Most abundant; primarily a feedback | Short (days) | Not assigned GWP (feedback) |
Note: GWP values can vary slightly between IPCC reports (AR5/AR6 shown). While CO₂ has GWP of 1, its volume and lifetime make it the primary contributor to current warming.
Historical Context & Scientific Understanding
The science of climate change has evolved over nearly two centuries, building on observations, experiments, and modeling.
1824: Joseph Fourier
Suggested Earth's atmosphere acts like a "greenhouse," trapping heat.
1859: John Tyndall
Identified that gases like water vapor and CO₂ absorb infrared radiation.
1896: Svante Arrhenius
Predicted doubling CO₂ could significantly warm Earth (est. 5-6°C).
1938: Guy Callendar
Linked observed early 20th-century warming to rising CO₂ from fossil fuels (the "Callendar Effect").
1958: Charles David Keeling
Began continuous CO₂ measurements at Mauna Loa, providing the "Keeling Curve" – undeniable proof of rising CO₂.
1988: IPCC Established
WMO and UNEP formed the Intergovernmental Panel on Climate Change for scientific assessments. James Hansen testified to US Congress about human-caused warming.
1992: UNFCCC Adopted
UN Framework Convention on Climate Change adopted at Rio Earth Summit.
1997: Kyoto Protocol
First legally binding GHG reduction targets for developed countries.
2015: Paris Agreement
Aims to limit warming well below 2°C, preferably 1.5°C, via Nationally Determined Contributions (NDCs).
2021 (IPCC AR6)
"It is unequivocal that human influence has warmed the atmosphere, ocean and land."
Indicators of a Warming Climate
Multiple lines of evidence confirm our world is warming:
Rising Global Temperatures
Significant increase in land and ocean surface temperatures. Past decade warmest on record.
Warming Oceans
Oceans absorbed >90% of excess heat, leading to rising temperatures, especially in upper layers.
Melting Ice & Snow
Retreat of glaciers/ice sheets, declining Arctic sea ice, decreasing snow cover, thawing permafrost.
Sea Level Rise
Caused by thermal expansion of water and melting land-based ice.
Changes in Precipitation
More intense rainfall/floods in some regions, more severe droughts in others.
Extreme Weather Events
Increased frequency/intensity of heatwaves, heavy precipitation, droughts, and some intense cyclones.
Ocean Acidification
Increased CO₂ absorption by oceans decreases seawater pH.
Shifts in Species Ranges
Biological indicators like changes in species distribution and timing of seasonal events (phenology).
UPSC Relevance
Understanding these fundamentals is crucial for Prelims and Mains (GS Paper I - Geography, GS Paper III - Environment, S&T).
Prelims Focus:
- Definitions: climate, weather, climate change, global warming.
- Greenhouse effect (natural vs. enhanced).
- Major GHGs (CO₂, CH₄, N₂O, F-gases): sources, GWP, lifetime.
- Historical milestones: Arrhenius, Keeling Curve.
- IPCC: role, key conclusions.
- UNFCCC, Kyoto Protocol, Paris Agreement: basic objectives.
- Indicators of warming.
Mains Focus (Sample Questions):
- "What is the difference between climate change and global warming? Explain the greenhouse effect and the role of major greenhouse gases."
- "Trace the historical evolution of scientific understanding of climate change and the key international responses."
- Answers on impacts, mitigation, or adaptation must build upon these basics.