Earth’s Fever: The Hottest Days Ahead and What They Mean for Humanity

Earth’s Fever: The Hottest Days Ahead and What They Mean for Humanity

The Earth’s rising average surface temperature is a critical issue with significant implications for humans, animals, and agriculture. TheBrink addresses your query by examining the historical context of Earth’s highest temperatures

Highest Temperature in Earth’s History

To identify the highest global mean surface temperature (GMST) in Earth’s history, we must look to paleoclimate records, as modern instrumental records only extend back to the 1850s. A comprehensive study provides this most detailed reconstruction of GMST over the past 485 million years, known as the PhanDA dataset. This study indicates that during the Phanerozoic Eon (the last 539 million years), Earth’s GMST reached as high as 36°C (96.8°F) during extreme greenhouse climates, notably during periods like the Early Eocene Climatic Optimum (EECO, ~50 million years ago). The most recent data available, based on global climate monitoring, indicates that the Earth’s global mean surface temperature (GMST) for 2024 was approximately 15.29°C (59.52°F) These temperatures were driven by elevated atmospheric carbon dioxide (CO₂) levels, often exceeding 1000–2000 parts per million (ppm), compared to today’s ~420 ppm.

What Happened During These Periods?

Climate and Environment: During the EECO, Earth was largely ice-free, with lush tropical forests extending to high latitudes, and polar regions supporting ecosystems with crocodiles and palm trees. Sea levels were up to 100 meters higher than today due to the absence of major ice sheets. Ocean circulation patterns were altered, and marine ecosystems were dominated by heat-tolerant species like corals and plankton adapted to warm conditions.

Life and Adaptation: Complex animal life thrived, but rapid warming events, such as the Paleocene-Eocene Thermal Maximum (PETM, ~55.5 million years ago), triggered significant ecological shifts. Some species, particularly smaller mammals, adapted through evolutionary changes, while others faced regional extinctions. Marine ecosystems experienced stress from ocean acidification and deoxygenation due to high CO₂ levels.

Relevance to Today: These ancient warm periods occurred over millions of years, allowing ecosystems time to adapt. In contrast, current human-driven warming is occurring at a rate unprecedented in the geological record (CO₂ increases at ~2–3 ppm per year vs. 0.0001 ppm per year in natural events), making adaptation far more challenging for modern species, including humans.

Modern Context and Recent Temperature Records

The modern instrumental record (since ~1850) shows that 2024 was the warmest year on record, with a GMST of approximately 15.29°C (59.52°F), or 1.29°C (2.32°F) above the 20th-century average (13.9°C) and 1.46°C (2.63°F) above the pre-industrial baseline (1850–1900). The hottest single day recorded was July 22, 2024, with a global average temperature of 17.16°C (62.89°F).

Drivers of Recent Warming:

Greenhouse Gases: Human emissions of CO₂, methane (CH₄), and nitrous oxide (N₂O) have increased atmospheric concentrations to levels not seen in millions of years, with CO₂ at ~420 ppm in 2024. These gases trap heat, driving the observed warming trend.

El Niño and Natural Variability: The exceptional warmth of 2023–2024 was amplified by a strong El Niño event, which typically elevates global temperatures by ~0.1–0.2°C for a year or two.

Other Factors: Reduced sulfur aerosol emissions from shipping (which previously had a cooling effect) and natural variability (e.g., ocean heat uptake) have contributed marginally to recent temperature spikes.

Predictions for Future Temperatures

Predicting the exact timing and magnitude of future temperature peaks is challenging due to uncertainties in emissions pathways, climate feedbacks, and natural variability. However, based on current trends, climate models, TheBrink provides the following projections for the GMST and when a new “highest temperature” might occur:

Near-Term (2025–2035):

2025 Outlook: Given the ongoing El Niño influence and the typical lag in peak temperature response, 2025 is likely to be as warm as or slightly warmer than 2024, with a GMST potentially reaching 15.3–15.5°C (59.5–59.9°F), or ~1.5°C above pre-industrial levels. A strong La Niña in late 2025 could temper this slightly, reducing temperatures by ~0.1°C.

1.5°C Threshold: The Paris Agreement aims to limit warming to 1.5°C above pre-industrial levels, but ThrBrink wont talk much about this. Current trends suggest the long-term average GMST will likely exceed this threshold very easily, assuming emissions continue at present rates. Individual years may temporarily exceed 1.5°C earlier (e.g., 2024 was close at 1.46°C).

Highest Temperature: A new daily or annual GMST record is probable within the next 5–10 years, potentially by 2030, with daily peaks possibly reaching 17.2–17.4°C (63.0–63.3°F) during summer months, driven by continued emissions and potential El Niño events. This would surpass the 2024 record of 17.16°C.

Mid-Century (2050–2070):

If emissions follow a high-emissions scenario (e.g., SSP5-8.5, akin to IPCC’s A2), GMST could reach 2–3°C (3.6–5.4°F) above pre-industrial levels by 2050–2060.

Under a moderate-emissions scenario (e.g., SSP2-4.5), warming may be limited to 1.8–2.5°C (3.2–4.5°F).

End of Century (2070–2100):

In a business-as-usual scenario (SSP5-8.5), warming could reach 4–5.4°C (7.2–9.7°F) by 2100, resulting in a GMST of 18–19.4°C (64.4–66.9°F). This would be the highest GMST in at least 2,000 years, approaching conditions last seen in the mid-Pliocene (~3 million years ago, GMST ~16–18°C).

With aggressive mitigation (SSP1-2.6, akin to IPCC’s B1), warming could be limited to 1.5–2°C, keeping GMST below 16°C (60.8°F).

Uncertainties:

Feedback Loops: Potential amplification from permafrost thaw (releasing methane), ice-albedo feedback (less reflective ice, more heat absorption), and cloud dynamics could accelerate warming beyond current model projections. Conversely, some feedbacks (e.g., increased cloud cover in certain regions) might have a cooling effect.

Human Actions: The trajectory depends heavily on global emissions policies. Swift reductions to net-zero CO₂ by 2050 could stabilize temperatures, while continued reliance on fossil fuels will make it hotter.

Data Gaps: Models can underestimate ice sheet melt rates or regional variability, and the unprecedented pace of current warming limits the applicability of paleoclimate analogs.

Impacts on Humans, Animals, and Agriculture

The consequences of rising temperatures will vary by region, ecosystem, and socioeconomic context. Below, TheBrink outlines what can happen (potential outcomes under different scenarios) and what is likely to happen (based on current trends and high-confidence projections).

Humans

What Can Happen:

Extreme Heat: In high-emissions scenarios, regions like parts of South Asia, the Middle East, and Sub-Saharan Africa could experience mean annual temperatures (MAT) exceeding 29°C (84°F) by 2070, conditions currently found in only 0.8% of Earth’s land surface (e.g., the Sahara). This could render areas uninhabitable without advanced cooling infrastructure, affecting 1–3 billion people depending on population growth and migration.

Health Impacts: Heatwaves could increase heatstroke and cardiovascular deaths, particularly in urban heat islands. Poor air quality from wildfires and ozone will add to respiratory issues. Tropical disease vectors (e.g., mosquitoes carrying malaria or dengue) may expand to new regions.

Displacement and Conflict: Sea level rise (projected at 0.6–4 feet by 2100, potentially higher with rapid ice sheet melt) could displace tens of millions from coastal cities. Competition for water and arable land may fuel conflicts, especially in vulnerable regions.

Economic Disruption: Extreme weather (e.g., hurricanes, floods) could cause trillions in damages annually. Labor productivity, especially in outdoor sectors like agriculture and construction, may decline due to heat stress.

What Will Likely Happen:

By 2030–2050, most regions will experience more frequent heatwaves, with urban areas facing heightened risks due to the heat island effect. Annual heat-related deaths could rise by tens of thousands globally, particularly among the elderly and low-income populations.

Sea level rise of 8–12 inches by 2050 will impact coastal communities, with increased flooding in places like Miami, Bangladesh, and Pacific island nations. Migration from vulnerable areas will likely increase, though barriers (e.g., economic, political) will limit large-scale relocation.

Food and water security will be strained in developing nations, particularly in Sub-Saharan Africa and South Asia, where infrastructure is less resilient. Wealthier nations may mitigate some impacts through adaptation (e.g., improved cooling, flood defenses), but costs will be significant.

Critical Evaluation and Caveats

Historical Context: While ancient warm periods provide analogs, the rapid rate of current warming (100–1000 times faster than natural events) limits their predictive power. Human systems (e.g., agriculture, urban infrastructure) are less adaptable than ancient ecosystems.

Model Uncertainties: Climate models may underestimate tipping points (e.g., ice sheet collapse, Amazon dieback) or overestimate stabilizing feedbacks (e.g., cloud cover). The 2023–2024 temperature anomalies, which defied predictions, highlight gaps in understanding short-term variability.

Socioeconomic Factors: Impacts depend on human responses, including adaptation capacity, political will, and economic resources. Wealthier nations may buffer some effects, while poorer regions face disproportionate risks.

The highest GMST in Earth’s history was ~36°C (~96.8°F) during the Early Eocene, a time of ice-free, tropical conditions driven by high CO₂. Today, we’re at ~15.3°C (59.5°F), with 2024 setting a modern record. Without aggressive mitigation, GMST could reach 16–17°C (60.8–62.6°F) by 2050 and 18–19.4°C (64.4–66.9°F) by 2100, unprecedented in human history. This would bring severe heatwaves, sea level rise, and ecosystem disruptions, disproportionately harming vulnerable human populations, animals, and agriculture.

-Chetan Desai (chedesai@gmail.com)