By Naeema Saleem — SCN NEWS
NEW YORK — António Guterres will leave the United Nations at the end of 2026 after a decade in which the office of Secretary-General was repeatedly asked to carry responsibilities far greater than the formal powers attached to it. From Russia's invasion of Ukraine and the Gaza war to climate disruption, displacement, pandemic recovery and the emergence of artificial intelligence as a geopolitical issue, Guterres has operated in an international system increasingly divided over both the rules it is supposed to uphold and the institutions meant to enforce them. As the race to choose his successor moves into the 81st session of the General Assembly, the more consequential question is therefore not simply who will become the tenth Secretary-General, but what kind of diplomatic authority can the next UN chief realistically exercise in a world where major powers increasingly resist multilateral restraint.
Guterres took office on January 1, 2017, after serving as Portugal's prime minister and spending a decade as UN High Commissioner for Refugees. He arrived promising conflict prevention, institutional reform and stronger international cooperation, but much of his tenure instead became a demonstration of the limits of multilateral power. A Secretary-General commands no military, possesses no Security Council veto and cannot impose sanctions or force governments to comply with international law. Yet the office carries significant convening authority, diplomatic access and the ability to place issues before the international community — powers Guterres repeatedly attempted to use when direct enforcement was unavailable.
Ukraine simultaneously demonstrated the other side of that equation. Guterres could invoke the UN Charter, condemn violations of international law, maintain channels with Moscow and Kyiv and facilitate humanitarian diplomacy, but he could not order Russian forces to withdraw. Russia's permanent membership and veto in the Security Council also exposed an institutional contradiction much larger than the Secretary-General himself: one of the governments whose conduct the UN system was being asked to confront possessed the power to block substantive Council action against itself. The conflict consequently showed how quickly the authority of the Secretary-General can reach its ceiling when a permanent Security Council member treats a core geopolitical interest as non-negotiable.
The Gaza war subjected the office to an equally severe test. Guterres repeatedly demanded protection for civilians, humanitarian access and a ceasefire while invoking international humanitarian law, but the intensity of the conflict and divisions among major powers again exposed the distance between moral and diplomatic authority and coercive power. His interventions could shape international debate and increase pressure for humanitarian action, but they could not dictate Israeli military decisions, compel Hamas to release hostages or independently produce the political settlement necessary to end the conflict. For his successor, Ukraine and Gaza leave the same uncomfortable lesson: the world often measures the Secretary-General against outcomes that only sovereign governments and, in some cases, veto-wielding powers can ultimately deliver.
Climate change was one arena where Guterres attempted to expand the political reach of the office rather than wait for formal authority. Across his tenure he transformed climate diplomacy into a central component of the Secretary-General's public agenda, repeatedly pressing governments to accelerate renewable energy, phase down dependence on fossil fuels, increase adaptation financing and address the disproportionate costs imposed on vulnerable countries. By 2026, his climate argument had expanded into energy security, economic competitiveness and technology, including pressure on artificial-intelligence companies to disclose the carbon, water and land footprints of data centres. He could not force governments to meet the Paris Agreement's targets, but he helped ensure that climate failure became increasingly difficult for governments to separate from discussions of development, finance and international security.
That institutional inheritance matters because the international environment facing Guterres' successor may be even less forgiving than the one he entered in 2017. Nuclear arms-control guardrails have weakened, geopolitical competition among the United States, China and Russia has intensified, humanitarian financing is under pressure and progress toward the Sustainable Development Goals remains badly off track. Climate impacts are accelerating at the same time governments face debt pressures and competing demands on public finances, while wars increasingly overlap with strategic competition among major powers. The next Secretary-General will therefore be expected to strengthen an institution whose political room for manoeuvre is narrowing precisely as the number and complexity of problems referred to it are increasing.
Artificial intelligence adds a category of challenge that barely existed in its present form when Guterres began his first term. The UN's Scientific Advisory Board has warned that AI and data systems are rapidly becoming system-level infrastructure affecting government, science, health and other sectors while international governance struggles to keep pace. The next Secretary-General will have to help build cooperation around technologies largely developed and controlled not by the United Nations but by powerful governments and private corporations, while navigating disputes over safety, economic advantage, military applications, information integrity and unequal access. The office that once concentrated overwhelmingly on war, peace, development and human rights is consequently acquiring an additional role in the governance of technologies capable of reshaping all four.
This is what makes the contest to replace Guterres more interesting than the mechanics of the appointment itself. The next UN chief must be independent enough to invoke the Charter against powerful governments, yet politically acceptable enough to survive a process in which the five permanent Security Council members — the United States, China, Russia, Britain and France — retain decisive influence. A viable candidate will need access to Washington without appearing subordinate to Washington, credibility with Beijing and Moscow without sacrificing the confidence of Western governments, and legitimacy across the Global South without becoming identified with a particular geopolitical bloc. The successful candidate will simultaneously be expected to act as diplomat, institutional manager, humanitarian advocate, climate voice, crisis negotiator and increasingly a global interlocutor on emerging technology.
Guterres' decade ultimately demonstrates why that combination is so difficult. His office could help move almost 33 million tonnes of food through a war zone but could not end the war surrounding the corridor; it could put climate action at the centre of international diplomacy but could not compel governments to meet their commitments; and it could demand respect for international law while lacking independent machinery to enforce that demand. His influence was greatest where governments still wanted a neutral intermediary and dramatically weaker where major powers concluded that compromise threatened fundamental strategic interests.
That record should shape how UNGA81 evaluates his successor. Selecting the next Secretary-General is not simply a search for the strongest administrator or most polished diplomat; it is a decision about who can preserve enough independence to make the office meaningful while retaining sufficient access to governments capable of paralysing it. Guterres will hand over the position on January 1, 2027, but he will also hand over unresolved wars, unfinished UN reforms, a deteriorating arms-control environment, a climate emergency, a development financing crisis and an emerging technological governance contest whose boundaries are still being defined.
The paradox is difficult to escape. The next Secretary-General will be expected to defend a multilateral system precisely when some of its most powerful members increasingly disagree over its rules, and will need the cooperation of the same governments the office may sometimes be required to challenge. After ten years of Guterres, that may be the most important lesson of the position: a UN chief does not control the world, but the effectiveness of the office depends on finding spaces where diplomacy can still influence it.