Lecture 2 - Global Mean Surface Temperature (GMST) PDF

ASUx31s Climate Change, Energy and Water Issues Fall 2024 Presented by Assistant Prof. Ahmed M. Abdulmohsen Lecture 2: Global Mean Surface Temperature (GMST) Tracking global warming and temperature anomalies...

ASUx31s Climate Change, Energy and Water Issues Fall 2024 Presented by Assistant Prof. Ahmed M. Abdulmohsen Lecture 2: Global Mean Surface Temperature (GMST) Tracking global warming and temperature anomalies 2 Outlines: Introduction to GMST Measuring GMST Historical Trends in GMST Factors Affecting GMST Energy Balance and GMST Examples Long-Term Temperature Trends and Projections Implications of Increasing GMST 3  Introduction to Global Mean Surface Temperature (GMST) Definition “The Global Mean Surface Temperature (GMST) is the average temperature of Earth’s surface, calculated by averaging measurements from various locations around the globe, both land and sea, over a period of time”. GMST is an important indicator of climate change and is used to track warming trends over time. 4  Measuring GMST Data Collection: GMST is derived from land-based weather stations, ocean buoys, and satellite measurements. Measurements are combined into a global dataset and averaged to account for seasonal and geographical variations. Major datasets for GMST include NASA's GISTEMP, the HadCRUT dataset from the UK Met Office, and NOAA's GlobalTemp. 5  Measuring GMST Anomalies: Instead of focusing on absolute temperatures, scientists often use temperature anomalies 𝑨𝒏𝒐𝒎𝒂𝒍𝒚 = 𝑶𝒃𝒔𝒆𝒓𝒗𝒆𝒅 𝑻𝒆𝒎𝒑𝒓𝒂𝒕𝒖𝒓𝒆 − 𝑩𝒂𝒔𝒆𝒍𝒊𝒏𝒆 𝑻𝒆𝒎𝒑𝒓𝒂𝒕𝒖𝒓𝒆 Where the baseline temperature is a reference period (often 1951- 1980) used to compare temperature changes over time. 6  Historical Trends in GMST Pre-Industrial Era: Before the Industrial Revolution (~1750), global temperatures remained relatively stable, with natural fluctuations. Post-Industrial Warming: Since the late 19th century, human activities (especially fossil fuel combustion) have caused a marked rise in GMST. Over the last century, the GMST has increased by approximately 1.1°C, with a notable acceleration in recent decades. 7  Historical Trends in GMST Over the last century, the GMST has increased by approximately 1.1°C, with a notable acceleration in recent decades 8  Factors Affecting GMST The GMST is influenced by several natural and anthropogenic factors: Natural Factors: 1.Solar Variability: 1. The Sun’s output varies over time, influencing Earth’s climate. However, these changes are small compared to human-induced effects. 2.Volcanic Activity: 1. Major volcanic eruptions release aerosols into the atmosphere, which reflect solar radiation and temporarily cool the Earth. 3.Ocean Circulation: 1. Large-scale ocean currents like the El Niño Southern Oscillation (ENSO) affect the global distribution of heat. 9  Factors Affecting GMST Anthropogenic Factors: 1.Greenhouse Gas Emissions: 1. The burning of fossil fuels, deforestation, and industrial activities increase the concentration of greenhouse gases (e.g., CO₂, CH₄), trapping more heat in the atmosphere. 2.Land Use Changes: 1. Urbanization and deforestation affect the albedo (reflectivity) of Earth’s surface, contributing to warming. 3.Aerosols: 1. Human activities also release aerosols that can either cool the Earth by reflecting sunlight or warm it by absorbing heat. 10  Factors Affecting GMST Factor Type Natural Factors Human-Driven Factors Solar Variability Changes in solar radiation due to sunspot cycles. N/A Major volcanic eruptions release aerosols that reflect Volcanic Activity N/A sunlight, causing temporary cooling. Large-scale ocean patterns (e.g., El Niño and La Ocean Circulation Niña) redistribute heat globally, influencing weather N/A and climate. Natural processes like volcanic eruptions and Human activities, such as fossil fuel combustion, Greenhouse Gas Levels wildfires can alter atmospheric greenhouse gas deforestation, and industrial processes, increase concentrations over long timescales. concentrations of CO₂, CH₄, and N₂O. Variations in Earth’s reflectivity due to ice cover Deforestation, urbanization, and land use changes Albedo Changes changes or desertification. lower the Earth's albedo, increasing heat absorption. Aerosols released from industrial activity, such as Naturally occurring aerosols from volcanic activity or sulfur compounds, can have cooling effects, while Aerosols desert dust can have cooling effects by reflecting black carbon (soot) from burning fossil fuels absorbs sunlight. heat and contributes to warming. 11  The Earth’s Energy Balance and GMST As discussed in the previous lecture the energy balance on Earth can be expressed as: 𝑰𝒊𝒏 = 𝑰𝒐𝒖𝒕 Whenever unbalance takes place the Earth's surface temperature is determined by the balance between incoming solar radiation and outgoing infrared radiation. This can be expressed mathematically as: ∆𝑭 ∆𝑻 = 𝝀 Where: ∆𝑻 ≡ 𝒕𝒉𝒆change in GMST ∆𝑭 ≡ 𝒕𝒉𝒆 radiative forcing 𝝀 ≡ 𝒕𝒉𝒆climate sensitivity parameter (how sensitive the climate is to changes in radiative forcing) 12  The Earth’s Energy Balance and GMST radiative forcing “the difference between incoming and outgoing radiation due to factors like greenhouse gases” ∆𝑭 = 𝑰𝒊𝒏 − 𝑰𝒐𝒖𝒕 Radiative forcing is measured in watts per square meter (W/m²) and represents how much energy is added to the Earth’s system. For example, the radiative forcing due to increased CO₂ levels can be estimated using the following logarithmic formula: 𝑪 ∆𝑭𝑪𝑶𝟐 = 𝟓. 𝟑𝟓 × 𝒍𝒏 𝑪𝟎 𝑪 ≡ 𝒕𝒉𝒆 current concentration of 𝑪𝑶𝟐 𝑪𝟎 ≡ 𝒕𝒉𝒆 pre−industrial concentration of CO₂ (about 280 ppm) 13  Example: Estimating Temperature Change Let the concentration of CO₂ doubles from 280 ppm to 560 ppm. Then, the radiative forcing would be: 𝑪 𝟓𝟔𝟎 ∆𝑭𝑪𝑶𝟐 = 𝟓. 𝟑𝟓 × 𝐥𝐧 = 𝟓. 𝟑𝟓 × 𝐥𝐧 = 𝟑. 𝟕𝟏 𝑾𝒂𝒕𝒕/𝒎𝟐 𝑪𝟎 𝟐𝟖𝟎 Now Assume the climate sensitivity factors if 0.8 (Watt/m2)/0C. Then, the change in GMST would be: ∆𝑭 𝟑. 𝟕𝟏 ∆𝑻 = = = 𝟒. 𝟔𝟒℃ 𝝀 𝟎. 𝟖 This means that a doubling of CO₂ would increase global temperatures by approximately 4.64°C if no other changes occur 14  Example: Calculating the GMST Anomaly If the observed temperature in 2020 was 14.9°C. Knowing that, the baseline average (1951-1980) was 14.0°C. then the 2020’s GMST Anomaly would be: 𝑨𝒏𝒐𝒎𝒂𝒍𝒚 = 𝟏𝟒. 𝟗 − 𝟏𝟒 = 𝟎. 𝟗 ℃ This indicates that the global mean surface temperature in 2020 was 0.9°C above the baseline average. 15  Long-Term Temperature Trends and Projections Historical Warming: The 20th century has seen an increase of about 1.1°C in GMST, with most of the warming occurring since the 1970s. Future Projections: Climate models project that, without significant reductions in greenhouse gas emissions, global temperatures could rise by 2 to 4°C by the end of the 21st century. IPCC (Intergovernmental Panel on Climate change – UN) Scenarios: RCP2.6: A scenario with aggressive mitigation could limit warming to 1.5-2°C. RCP8.5: A “business-as-usual” scenario could result in warming of 4°C or more. RCP→ Representative Concentration Pathway 16  Long-Term Temperature Trends and Projections IPCC (Intergovernmental Panel on Climate change – UN) Scenarios: RCP2.6: A scenario with aggressive mitigation could limit warming to 1.5-2°C. RCP8.5: A “business-as-usual” scenario could result in warming of 4°C or more. RCP→ Representative Concentration Pathway 17  Long-Term Temperature Trends and Projections The rise in GMST leads to significant climate impacts: Melting Ice: Increased temperatures lead to the melting of polar ice caps and glaciers, contributing to sea level rise. Heatwaves: More frequent and intense heatwaves occur due to rising GMST. Shifts in Weather Patterns: Changes in precipitation patterns, more intense storms, and longer droughts. Ecosystem Disruptions: Coral reefs, forests, and marine ecosystems are vulnerable to temperature shifts. 18  Conclusion To conclude today’s Lecture Global Mean Surface Temperature (GMST) is a key indicator of climate change. Understanding the historical trends and the factors influencing GMST allows us to predict future climate changes and their potential impacts. By calculating the relationship between radiative forcing and temperature, we can estimate the consequences of increased greenhouse gas emissions and the urgency of climate action. 19  End of lecture 2 Thanks for your Attention Any Questions Assistant prof. Ahmed M. Abdulmohsen [email protected]