The Earth's climate has exhibited marked "natural" climate changes, with time scales varying from many millions of years down to a few years. For example:

Greenhouse gases have continued to increase in the atmosphere. This is due largely to human activities, mostly fossil fuel use, land-use change, and agriculture. About 63% of the warming effect of greenhouse gas increases over the last 200 years is due to carbon dioxide.

The NIWA-operated National Rivers Water Quality Network (NRWQN) is New Zealand's only national water quality monitoring tool.

Future climate changes will be affected, amongst other things, by how much extra greenhouse gas goes into the atmosphere. For this reason, NIWA has looked at likely changes in New Zealand across six greenhouse gas emission scenarios from the Intergovenmental Panel on Climate Change (IPCC), but focusing on the mid-range. These scenarios do not include major efforts to reduce greenhouse gas emissions.

Life cycle of an iceberg
Icebergs are biggest when they calve from the ice shelf. After that, the sun and the ocean start to melt the iceberg. Waves erode its sides and small pieces of ice constantly break off. But perhaps the most dramatic way that icebergs get smaller is by splitting, from waves flexing the iceberg, or losing their rams. Rams are portions of an iceberg that jut out horizontally from an iceberg underwater. These can break away and surge to the surface under their own buoyancy. An iceberg’s route is determined by the action of wind, waves, and ocean currents.

A powerful Magnitude 8.0 earthquake ruptured the seafloor south of Samoa on 30 September 2009, unleashing a destructive tsunami on Samoa, American Samoa, and northern Tonga (Niuatoputapu). Its impact on distant New Zealand shores was picked up by a sea-level monitoring system operated by NIWA and other agencies. The system showed that peak waves arrived between 1–2 and 13 hours after the arrival of the first tsunami waves, depending on locality.

El Niño is a natural feature of the global climate system. Originally it was the name given to the periodic development of unusually warm ocean waters along the tropical South American coast and out along the Equator to the dateline, but now it is more generally used to describe the whole "El Niño - Southern Oscillation (ENSO) phenomenon", the major systematic global climate fluctuation that occurs at the time of an "ocean warming" event. El Niño and La Niña refer to opposite extremes of the ENSO cycle, when major changes in the Pacific atmospheric and oceanic circulation occur.

A mixing zone is a designated area of a stream or river into which wastewater is permitted to empty.

Reasonable mixing is the amount of pollutant that can be discharged into a mixing zone.