UNDERSTANDING 2 o C  And why slipping off 2 really matters

The document argues that global average temperature targets like 2°C are simplistic indicators that mask local climate extremes and probabilistic risks. It details three types of emissions pathways to achieve these targets, noting that 'likely' chances of staying below 2°C often depend on high reduction rates or the feasibility of negative emissions technologies like BECCS. It further asserts that meeting a 1.5°C goal necessitates significant negative emissions in the latter half of the century.

• A global average temperature increase of 2°C is an indicator of local changes and does not reflect actual conditions 'on the ground'; it can result in much higher temperature changes for specific land masses depending on latitude and altitude.
• Temperature targets are based on probabilities rather than certainties. A 'likely chance' of staying below 2°C is defined as a probability higher than 66%, while a 'medium chance' is between 50-66%.
• Small shifts in emissions pathways can significantly increase the risk of extreme warming. For example, a pathway with a 50% probability of a 2.5°C rise may have a risk of exceeding 3.0°C that is more than triple that of a pathway with a 50% probability of a 2.0°C rise.
• There are three theoretical pathways to 2°C: Type I (early, lower peak with moderate-high reductions), Type II (later, higher peak with very high reductions), and Type III (later, higher peak with high reductions and substantial negative emissions).
• Type II pathways are generally not considered feasible for a 'likely' chance of staying below 2°C due to practical constraints related to the lifetimes of infrastructure and machinery, such as power stations (approx. 40 years) and building stock.
• Achieving a 'likely' chance of staying below 2°C in Type III scenarios requires negative emissions, primarily through Bio-Energy combined with Carbon-Capture-and-Storage (BECCS), which removes CO2 from the air by storing biomass oxidation products underground.
• No modelled emissions pathways of Type I or Type II provide a 'likely chance' of meeting a 1.5°C goal; this target requires significant negative emissions in the second half of the century to recover after an initial overshoot.

APA

Ward, M. (n.d.). UNDERSTANDING 2 o C  And why slipping off 2 really matters. Climate Strategies. https://climatestrategies.org/wp-content/uploads/2014/11/understanding-2-degrees-c-final-28-feb-10.pdf

Chicago

Ward, Murray. UNDERSTANDING 2 o C  And why slipping off 2 really matters. Climate Strategies, n.d. https://climatestrategies.org/wp-content/uploads/2014/11/understanding-2-degrees-c-final-28-feb-10.pdf.

Wikipedia

{{cite report |last1=Ward |first1=Murray |title=UNDERSTANDING 2 o C  And why slipping off 2 really matters |publisher=Climate Strategies |url=https://climatestrategies.org/wp-content/uploads/2014/11/understanding-2-degrees-c-final-28-feb-10.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{wardndunderstanding, author = {Ward, Murray}, title = {{UNDERSTANDING 2 o C  And why slipping off 2 really matters}}, institution = {Climate Strategies}, url = {https://climatestrategies.org/wp-content/uploads/2014/11/understanding-2-degrees-c-final-28-feb-10.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }