Research into city living and its impacts is burgeoning, thanks to the fact that more than half of us now live in urban areas. In this web focus we compile a number of papers documenting some of the challenges associated with city life, and some of the less expected outcomes.

Future sea-level rise is uncertain, not least because it is unclear how, and how fast, the ice sheets in Greenland and Antarctica are going to respond to ocean and atmosphere warming. This collection of research papers, overview articles and opinion pieces highlights current understanding of the sensitivity of the planet's cryosphere to temperature rise, including a view back into the past and far into the future.

Understanding the amplitude of climate variability in the past, as well as the causes and mechanisms responsible for this variability is important in its own right. Yet it also helps us get a better idea of the range of possible Earth system responses to human-induced greenhouse gas emissions. In this web focus we explore the links between past climate and carbon cycle perturbations, along with the ability of state-of-the-art climate models to capture these links.

Deep-sea carbon cycling is poorly constrained, not least because this remote environment is so difficult to explore. In this web focus we highlight the prevalence and diversity of seabed carbon sources.

The January 2010 Haiti earthquake was catastrophic, leaving one million homeless. In this focus issue we have gathered articles — ranging from primary research to opinion pieces — that explore the physical processes responsible for the earthquake and the damage caused, as well as the humanitarian problems now facing the poorest country in the western hemisphere.

Soil is one of the most precious resources on the planet. As the global population grows, and the climate continues to warm, the structure and function of soils could change. In this focus issue we have gathered articles — ranging from primary research to opinion pieces — that explore the sensitivity of soils to climate and land use change, and that highlight the key role that soils play in shaping the environment and human society.

Arsenic-contaminated groundwater endangers the health of millions of people in southern Asia. In this focus issue we gather together articles on the origin and fate of arsenic in groundwater, together with opinion pieces outlining options for dealing with the problem, and backstories detailing some of the challenges faced by the researchers.

As the world's leaders are getting ready to negotiate a new climate treaty in Copenhagen, there is No. sign of a long-term reduction in human-made carbon dioxide emissions. As a result, carbon sequestration may turn out to be our only option for controlling climate change. In this focus we collect articles that cover emissions budgets of carbon dioxide and other greenhouse gases and options for sequestration, as well as commenting on the difficult choices we are going to face in combating climate change.

In their report published in 2007, the Intergovernmental Panel on Climate Change projected that sea level is likely to rise between 18 and 59 centimetres by 2100, threatening the homes and livelihoods of millions who live in low-lying and deltaic regions. This focus draws together studies of past and present sea-level change, and predictions for future fluctuations, as well as presenting insights into the challenges facing coastal communities.

Our eternal quest to explore space continues to take us where No. humans have gone before. But while we push the frontiers of the Solar System, seeking to launch spacecraft to Europa and Ganymede, we are also rediscovering our relationship with the Moon. This Focus provides a glimpse into what we know, and do not know, about planetary bodies.

January 2009 marks the first anniversary of the launch of Nature Geoscience. To celebrate, we have put together our favourites from the first 12 issues. The selection, which is free for the months of January to March, reflects the breadth of topics covered byNature Geoscience, and the diversity of article styles. We hope you enjoy it.