Not every 1.5 degrees is the same promise

Climate coverage is dense with numbers. 1.5°C, 2°C, 2050, net zero, a 43 per cent cut. Each looks simple on its own, yet the same figure points at different things from sentence to sentence. A 1.5 that is a goal, a 1.5 that is a projection, and a 1.5 that is a threshold are three different statements.

This is not an attempt to judge climate targets. It is an attempt to sort the numbers in climate reporting by what each one actually measures. Once they are sorted, reports that looked contradictory turn out to have been describing different things.

What the Paris Agreement actually says

The Paris Agreement was adopted by 195 Parties at COP21 on 12 December 2015 and entered into force on 4 November 2016. As of 27 January 2026 there are 194 Parties. That the number is one lower than at adoption tells you something about the nature of the regime.

The temperature goal is usually compressed to "1.5 degrees," but the original has two layers. It holds the increase in global average temperature to "well below 2°C above pre-industrial levels" and pursues efforts "to limit the temperature increase to 1.5°C above pre-industrial levels." The first is what is to be held; the second is what is to be pursued. The two carry different legal weight.

What limiting warming to 1.5°C requires is also given numerically: greenhouse gas emissions must peak before 2025 at the latest and decline 43 per cent by 2030. When that figure appears in an article, it is worth asking whether it is a target, a requirement, or a current trend. The 43 per cent is the second of those, not the third.

The gap between pledges and policies

The two things most often blurred in climate numbers are pledges and policies. The emission targets countries file with the UN are Nationally Determined Contributions, or NDCs. Those are what has been said. The laws and measures actually in force are a separate matter.

The UN Environment Programme's Emissions Gap Report 2025 sets the two side by side. Assuming full implementation of NDCs, projected warming this century is 2.3–2.5°C. Calculated from current policies alone, it is 2.8°C. That is a difference of 0.3 to 0.5 degrees for the same planet, and that difference is the distance between what has been said and what is being done.

So a report saying "the world is heading for 2.8°C" and one saying "the world is heading for 2.4°C" are not in conflict. One is on current policies, the other assumes every pledge is kept. When an article omits that premise, finding it is the first thing to do.

The arithmetic of a tenth of a degree

The 2025 Emissions Gap Report looks like an improvement on the year before. The previous report projected 2.6–2.8°C on NDCs and 3.1°C on current policies, so both figures have come down.

The report then dissects its own improvement. 0.1°C of it comes from methodological updates, and the forthcoming withdrawal of the United States from the Paris Agreement will cancel another 0.1°C. Subtract both and the new NDCs themselves have produced almost no change. The report's own phrase is that they have "barely moved the needle."

This is the most practical habit in reading climate numbers. When a figure improves, ask whether the world improved or the method of counting changed. Both move the number the same way and mean opposite things.

A percentage cut means nothing without a base year

"A 55 per cent reduction" carries no information by itself, because it omits what the reduction is measured against.

The 2025 report states that cuts of 35 per cent and 55 per cent by 2035, compared with 2019 levels, align with the 2°C and 1.5°C pathways respectively. The base year here is 2019. Other documents use 1990, or 2005, or 2013. The higher the base year's emissions, the easier the same percentage becomes.

Target years hide a similar trap. A 2030 goal and a 2050 goal differ not only in difficulty but in political character. 2030 falls within or near the term of the government setting it; by 2050 almost everyone making today's decisions will have left office. It is not unusual for the same country to set an ambitious 2050 target and a conservative 2030 one, which is why the nearer target usually reveals more about the actual trajectory.

This is why articles placing one country's "40 per cent cut" beside another's usually are not comparing anything. Check first whether the base year and the target year match. A reduction figure quoted without both — the target year (2030? 2035? 2050?) and the base year (1990? 2019?) — is not a readable number.

"Overshoot," a word that has arrived recently

A term that has become common in climate documents in the past few years is overshoot. Instead of a binary of holding 1.5°C or failing, it describes a path that exceeds the level temporarily and then comes back down.

Given the size of the cuts required, the time remaining and the political climate, the 2025 report states that "a higher exceedance of 1.5°C will happen, very likely within the next decade," and goes on to frame the task as limiting the size of that overshoot.

This shift affects how headlines should be read. "1.5°C has been breached" and "1.5°C is still within reach" can appear in the same week. The first usually refers to an observed value for a particular year; the second to a long-term average and a return pathway. Neither is false, and neither is talking about the same thing.

Net zero by 2050 — net zero of what?

Target years carry the same problem. What "net zero by 2050" covers varies enormously with which emissions are in scope.

The International Energy Agency published Net Zero Emissions by 2050: A Roadmap for the Global Energy Sector in May 2021 and updated it in 2023. As the title says, this is a pathway for the energy sector. It is not an accounting of every greenhouse gas across the whole economy. Emissions from agriculture, land use and industrial processes are handled in other frameworks.

A second distinction sits on top of that. National net zero pledges are generally framed around emissions produced within a country's own territory. The share emitted elsewhere to manufacture imported goods does not appear. So the same phrase, "net zero by 2050," means different things depending on whether it covers the energy sector or the whole economy, and whether it is counted on a territorial or a consumption basis.

The IEA called its 2021 roadmap "a narrow but feasible pathway." In the meantime, energy-sector carbon dioxide emissions set a new record in 2022. A shared target year does not mean a shared promise.

Four questions to ask of any climate number

First, is it a goal or a projection? 1.5°C is what the agreement pursues; 2.8°C is where current policies point. Same unit, different kind of statement.

Second, is it pledge-based or policy-based? As of 2025, the value assuming all NDCs are met and the value from policies in force differ by 0.3 to 0.5 degrees.

Third, what is the base year? A percentage cut without one cannot be interpreted. Fifty-five per cent against 2019 and fifty-five per cent against 1990 are entirely different tasks.

Fourth, if the number moved, what moved? Emissions, the methodology, or the set of participating countries? The 2025 report separates all three explicitly.

Reading climate coverage is largely a matter of reconciling units. Check that two numbers are the same kind of number before comparing their size, and most of the apparent contradictions line up.

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