Two weeks after the Paris Climate Change Agreement officially came into force - marking the first time that governments have agreed legally binding limits to global temperature rises - the leaders of 195 countries are meeting in Marrakech for a critical climate change conference. Faced with the momentous task of implementing the commitments made in Paris last year, and reeling from a shock US Presidential election result, which could put the accord in jeopardy, leaders are set for a challenging few days.

A key test of this summit's outcome will be the extent to which climate negotiators and leaders manage to integrate climate change goals into our broader sustainable development agenda: neither set of goals can be achieved without the other; both are about rising above narrow national interests and committing to a shared vision of the future. Above all, the driving force behind both can be encapsulated in the single powerful pledge to 'leave no one behind'.

This pledge appears no less than six times in the declaration made by world leaders when we agreed the 2030 Agenda for Sustainable Development last year and it has quickly emerged as one of the most powerful means of framing our new approach to inclusive development. When we committed to the Global Goals , we committed to reach the furthest behind first; we signed up to listen to their voices, to involve them in designing policies that promote inclusion and challenge the social barriers that deny opportunity and limit potential; we promised to ensure that development would address - first and foremost - all forms of discrimination and exclusion, whether on the basis of gender, age, location, caste, religion, disability or sexual identity.

Of course, in many ways, reaching the poorest first is an old promise unmet. One of the weaknesses of the Millennium Development Goals (MDG) framework was its blindness to inequality and the most marginalised in our societies. Its focus on aggregate figures and overall progress failed to take into account growing social and economic disparities, while incentivizing states and large NGOs to prioritise big-picture wins. Even as overall poverty levels fell, inequality increased and the standard of living for the poorest and most marginalised worsened significantly.

Take India, for example, often held up as an exemplar of economic growth using basic income level measures. Research from our partners at Development Initiatives shows that the proportion of the Indian population who find themselves in the poorest 20 per cent globally has grown from 16 per cent to 38 per cent in the last 25 years. In the same time period, the absolute gap between the poorest 20 per cent globally and the rest of the world has widened significantly. As our colleagues at Oxfam have shown, runaway inequality has created a world in which 62 individuals now own as much as the poorest half of the world's population .

The SDGs force us to look beyond income. They compel us to tackle social and political marginalization, as well as economic; to amplify the voices of those who aren't heard; to create a system in which people are empowered to shape their own communities.

And when it comes to approaching climate justice, 'leaving no one behind' offers an equally powerful framework. Socially, economically, politically, or otherwise marginalised people are most vulnerable to climate disruption. When they have done the least to cause the problem, these people are suffering first and worst from the consequences of climate change. In all actions designed to foster climate justice, they must be our priority. Official UN estimates put the cost of achieving sustainable development at US $5-7 trillion per year, a large slice of which must fund the transition to a low-carbon world economy.

So too at the implementation level, we can no longer afford to treat climate action and sustainable development as two distinct agendas to be pursued in tandem. Well-designed policies and actions to reduce emissions and enhance resilience to climate disruptions can deliver broad sustainable development benefits. Similarly, advancing progress towards the SDGs can contribute to climate impact mitigation and adaptation. In Niger, for example, poor literacy and numeracy levels in rural areas have been identified as a significant barrier to disseminating the technologies needed for climate-smart agriculture and land management . By improving access to education, we can lay the necessary foundations for achieving our climate goals. For too long anti-poverty strategies and programs designed to protect the environment have been designed separately, often leading to conflict on the ground, wastage of scant resources and adverse impacts on both sides.

Leaders meeting in Marrakech this week have an opportunity to bring the two agendas together. This will not only be critically important from the point of view of maximizing funding, catalyzing information-sharing and data development and streamlining planning, budgetary and monitoring processes; it represents a vital opportunity to tell the shared story of these two agendas, to build a powerful new narrative around our collective plans to achieve sustainable, inclusive, development. The notion of 'leaving no one behind' has the potential to engage and motivate people in a way that a list of 17 Goals and 169 targets cannot, as well as offering a simple, effective way of holding governments to account. Ultimately, I believe it will be the true test of our new development agenda's transformative potential. Over the next couple months, as part of the Leave No One Behind Partnership we'll be sharing a series of powerful untold stories from people facing the worst levels of poverty, marginalisation and exclusion. The series will put the needs of those most in need in the context of the specific commitments enshrined in the UNs Sustainable Development Goals and Paris Climate Agreement.