Beyond the Numbers: The Emotional Impact of the 1.5°C Climate Threshold

Understanding Pre-Industrial Averages

The term “pre-industrial” is crucial in climate discussions. For instance, the NOAA global surface temperatures for September 2023 were 1.44 degrees Celsius above the 20th-century average. This “average” is often defined as a period before human activities significantly increased atmospheric greenhouse gases.

Most historical references place the Industrial Revolution between the mid-1700s and mid-1800s. However, scientific definitions of “pre-industrial” often span from 1850 to 1900. This period provides the earliest reliable surface temperature records.

Different research groups may use distinct parts of this time range. For NOAA, the “pre-industrial” period currently spans from 1850 to 1900. This helps in creating a consistent baseline for global temperature comparisons.

Despite slight variations in defining “pre-industrial,” the term essentially distinguishes human-induced climate changes from natural variability over millennia. This distinction is essential for understanding current climate trends.

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Deciphering Surface Temperature

Global surface temperature measurements can vary based on the method and location. On land, temperatures are recorded at ground level and two meters above. Over oceans, temperatures are measured directly by ships and buoys, as well as two meters above the water.

Satellites add another layer, estimating temperatures based on thermal and microwave energy. Despite varied measurement methods, all major temperature records consistently show a long-term warming trend.

When discussing the 1.5°C threshold, consider three key questions: the dataset used, the “pre-industrial” period defined, and the type of temperature measured. These factors help contextualize and compare different climate reports.

The NOAA Global Surface Temperature dataset, for example, blends sea surface temperatures with near-surface air temperatures to provide a comprehensive view of global warming trends.

The Historical and Diplomatic Significance

In the 1970s and 1980s, scientists used various temperature thresholds, typically between 1-2°C, to assess the impact of greenhouse gas emissions. These early studies laid the groundwork for international climate agreements.

The 1992 international climate treaty aimed to stabilize greenhouse gas levels to prevent dangerous climate interference. By 2010, the Cancun Agreement aimed to keep global temperature increases below 2°C above pre-industrial levels.

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However, further research indicated that vulnerable ecosystems and countries faced severe risks with even less than 2°C of warming. This led to the 2015 Paris Agreement, where nations pledged to limit temperature increases to 1.5°C, significantly reducing climate risks.

The 2018 IPCC Special Report on Global Warming of 1.5°C emphasized that limiting warming to 1.5°C would mitigate impacts on human and natural systems, highlighting the urgency of achieving this target.

Recognizing When We Cross the Threshold

The Paris Agreement’s 1.5°C threshold is not a simple day, month, or year benchmark. Instead, it reflects a consistent human-caused warming pattern. Temporary spikes, influenced by natural factors like El Niño, do not signify a permanent shift.

For example, global temperatures in late 2023 exceeded 1.5°C above pre-industrial levels. This does not mean the Paris Agreement has failed; natural and human factors combined can cause brief temperature surges.

Long-term trends, averaged over 20 to 30 years, provide a clearer picture of whether we have crossed the 1.5°C threshold. This method smooths out short-term fluctuations and reveals enduring climate patterns.

The Paris Agreement does not specify the number of years for this long-term trend or the dataset to use, leading to varied conclusions among scientists and governments.

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Impacts Beyond 1.5°C

Climate impacts do not start at 1.5°C; they are already being felt worldwide through extreme weather events. The 1.5°C threshold is not an on-off switch but a marker where risks amplify with each additional degree of warming.

The Paris Agreement’s 1.5°C target is based on models and historical data. Beyond this level, some ecosystems and regions face unacceptably high risks, especially those least responsible for emissions.

Temperature changes are not uniform globally. Projections show varying impacts for the hottest days and coldest nights with 1.5°C and 2°C of warming, highlighting the importance of urgent climate action.

Like a highway speed limit, the 1.5°C limit is set to prevent intolerable risks. Every bit of warming increases dangers, so it’s crucial not to exceed this threshold to avoid severe consequences.

Near-Term Climate Predictions

Climate models predict that global temperatures will remain high through early 2024, with a slight decline as El Niño conditions weaken. These models help us understand short-term climate dynamics.

Monthly temperatures in late 2023 were significantly above pre-industrial levels. Projections suggest a slight temperature drop in early 2024, yet levels will remain historically high.

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Medium-Term Climate Outlook

The World Meteorological Organization forecasts a 66% chance of annual global temperatures exceeding 1.5°C at least once between 2023-2027. This aligns with expectations of ongoing global warming trends.

The 6th Assessment Report indicates that global warming will likely reach 1.5°C between 2021 and 2040. This underscores the urgency of achieving net zero greenhouse gas emissions and enhancing resilience to climate impacts.