LIMITING OVERSHOOT

LIMITING OVERSHOOT
Why in News?
A new UNEP report, Limiting Overshoot, says temporarily exceeding the 1.5°C warming threshold is increasingly unavoidable, with warming potentially peaking around 1.8°C even under an optimistic scenario.
What is the 1.5°C Target?
•    The 1.5°C target refers to the goal of limiting the increase in global average temperature to 1.5°C above pre-industrial levels.
•    It emerged as an important climate-policy objective under the Paris Agreement of 2015.
•    Under Article 2 of the Paris Agreement, countries committed to holding the increase in global average temperature well below 2°C above pre-industrial levels while pursuing efforts to limit it to 1.5°C.
•    The 1.5°C level is not considered a completely safe level of warming; rather, limiting warming closer to this level reduces the severity of climate risks.
Why is 1.5°C Important?
•    Climate risks increase with every additional fraction of a degree of warming.
•    Compared with 2°C of warming, limiting warming to 1.5°C substantially reduces risks associated with extreme heat, drought, water stress and other climate impacts.
•    Higher warming also increases the risk of potentially irreversible changes involving ice sheets, the Amazon rainforest, permafrost and ocean circulation systems.
•    Therefore, the 1.5°C target represents an effort to minimise climate risks rather than eliminate them completely.
Evolution of the 1.5°C Target
•    For many years, 2°C was widely used as the benchmark for identifying dangerous climate change.
•    Economist William Nordhaus had argued that warming beyond 2°C could push living conditions outside the range experienced by human civilisation.
•    The Cancun Agreements at COP16 formally incorporated both 2°C and 1.5°C into an international climate framework.
•    The Paris Agreement subsequently established keeping warming well below 2°C as the central goal while identifying 1.5°C as the more desirable limit because climate risks are significantly lower at this level.
What is Climate Overshoot?
•    Climate overshoot refers to a situation in which global warming temporarily rises above a specified temperature threshold before potentially declining later.
•    In this context, an overshoot means warming rises above 1.5°C, remains above it for some period and is subsequently reduced through sustained climate action.
•    A temporary exceedance for a few months or even one or two years does not automatically mean that the Paris Agreement's 1.5°C goal has been breached.
•    The Paris temperature goal concerns long-term global warming measured over decades, rather than the temperature recorded during a single calendar year.
What does the Latest UNEP Report Say?
•    UNEP's Limiting Overshoot report considers crossing the 1.5°C threshold increasingly unavoidable.
•    Even under an optimistic scenario in which governments fully implement their existing climate plans and net-zero pledges, global warming could peak at around 1.8°C.
•    The report therefore argues that climate policy must prepare for an overshoot pathway rather than assuming that the world will remain below 1.5°C.
•    However, the report does not suggest abandoning the 1.5°C goal.
•    Instead, countries should aim to keep the overshoot as small and as short-lived as possible and subsequently bring temperatures down.
From “Below 1.5°C” to “Back Towards 1.5°C”
•    The emerging approach is to treat 1.5°C as a level that may be approached from above rather than achieved permanently from below.
•    This means the immediate priority remains massive reductions in greenhouse-gas emissions.
•    The world should minimise both the peak temperature reached and the length of time spent above 1.5°C.
•    The smaller and shorter the overshoot, the lower the expected damage and the better the possibility of eventually returning below 1.5°C.
Why Does the Extent of Overshoot Matter?
•    A larger or longer overshoot would increase the severity of climate impacts.
•    Prolonged higher temperatures can increase risks of extreme heat, wildfires, glacier loss and ecosystem damage, including damage to coral reefs.
•    Some climate changes may become difficult or impossible to reverse, even if global temperatures subsequently decline.
•    Rapid reductions in methane and other short-lived climate pollutants can help slow warming relatively quickly and reduce the extent of overshoot.
Some Damage May Not Be Reversible
•    Returning global temperatures below 1.5°C would not automatically reverse all the damage caused during the overshoot period.
•    Risks include major changes to the Greenland and West Antarctic ice sheets, the Amazon rainforest and the Atlantic Meridional Overturning Circulation (AMOC).
•    Sea-level rise, species extinctions and ecosystem shifts may continue even after global temperatures begin to decline.
•    Therefore, temperature reduction after an overshoot cannot be treated as equivalent to avoiding the overshoot altogether.
Mitigation: The Three-Stage Response
Immediate Phase
•    Countries need to rapidly reduce greenhouse-gas emissions while protecting vulnerable people and ecosystems.
•    Immediate emission reductions are essential to keep the eventual temperature peak as low as possible.
Peak-Warming Phase
•    At the point of peak warming, the world would need to reach at least net-zero emissions while simultaneously dealing with severe climate impacts.
•    Adaptation would become particularly important for protecting people, infrastructure and ecosystems.
Post-Peak Phase
•    Bringing temperatures down after the peak would require sustained net-negative CO₂ emissions.
•    This means removing more carbon dioxide from the atmosphere than is being emitted.
Role of Carbon Dioxide Removal
•    Carbon dioxide removal (CDR) would become increasingly important in an overshoot scenario.
•    However, the report indicates that even optimistic deployment of CDR is unlikely to reverse more than a few tenths of a degree of warming this century.
•    Afforestation and forest management alone would take more than 100 years to reduce warming by just 0.1°C, assuming there are no residual CO₂ emissions.
•    Therefore, carbon removal cannot substitute for rapid emissions reduction and should instead complement mitigation efforts.
Mitigation and Adaptation Must Go Together
•    Mitigation aims to reduce greenhouse-gas emissions and limit future warming.
•    Adaptation aims to reduce vulnerability to climate impacts that are already occurring or expected.
•    The report stresses that both approaches need to operate together.
•    Weak mitigation increases future warming and makes adaptation more difficult and expensive.
•    Poor adaptation, in turn, can leave people, infrastructure and ecosystems exposed even when mitigation improves.
Unequal Burden of Climate Overshoot
•    The effects of climate overshoot will not be distributed equally across countries and communities.
•    Countries that have contributed relatively little to historical global warming can nevertheless face high exposure and vulnerability to climate impacts.
•    This creates an important issue of climate equity and adaptation finance.
•    The material highlights the concern raised at COP30 in Belém, Brazil, regarding the need to substantially increase adaptation finance for developing countries.
•    UNEP had estimated that developing countries' adaptation needs could exceed $310 billion per year by 2035, around 12 times current international public finance flows.
1.5°C vs 2°C: Why the Difference Matters
•    1.5°C is not a “safe” threshold, but it represents a lower-risk climate pathway than 2°C.
•    Moving from 1.5°C towards 2°C increases the severity and likelihood of several climate impacts.
•    The distinction therefore reflects a risk gradient rather than a simple safe-versus-dangerous divide.
•    Every fraction of a degree avoided can reduce potential damage to people, ecosystems and climate-sensitive systems.