What you'll learn

• How climate has changed from the start of the Quaternary period to today.
• The difference between cold glacial periods and warmer interglacial periods.
• The key warming and cooling periods since 1000 AD.
• How evidence such as ice cores, tree rings, paintings, diaries and global temperature data helps prove climate change.

Start with the basics: weather, climate and time

Weather is what the atmosphere is doing in a place over a short time: today’s temperature, rainfall, wind and cloud. Climate is the long-term average pattern of weather, usually measured over 30 years or more.

Climate change means a long-term shift in average conditions. This can include changes in temperature, rainfall, ice cover, sea level and extreme weather patterns.

The key idea for this section is that Earth’s climate has never been completely fixed. It has changed naturally over millions of years, but the recent warming is unusually fast and is measured very clearly by modern data.

The Quaternary period: the big timeline

The Quaternary period is the most recent geological period. A geological period is a named block of Earth’s history used by scientists to organise deep time.

The Quaternary is split into two main parts:

• Pleistocene Epoch: from about 2.6 million years ago to 11,700 years ago.
• Holocene Epoch: from about 11,700 years ago to today.

The Pleistocene had repeated cold stages and warm stages. The Holocene is the warm interglacial period we live in now.

During glacial periods, huge ice sheets covered parts of North America, northern Europe and Asia. In the last glacial period, ice covered much of Scotland, Wales and northern England. Sea levels were lower because so much water was stored as land ice.

Use this timeline to keep the whole topic in order.

Key climate periods since 1000 AD

The spec also wants you to know the main warming and cooling periods over the last 1,000 years. Here, the time scale is much shorter than the whole Quaternary, so we use evidence such as tree rings, written records, paintings and modern temperature data.

AD is the calendar dating system used in the specification. 1000 AD means about 1,000 years after year 1.

Medieval Warm Period

The Medieval Warm Period, sometimes called the Medieval Climate Anomaly, lasted roughly from 950 to 1250 AD. Some areas, especially around the North Atlantic and parts of Europe, experienced warmer conditions.

Evidence includes tree rings, historical documents and signs of farming or settlement changes, such as Norse settlement in Greenland. However, it was not equally warm everywhere.

Little Ice Age

The Little Ice Age was a cooler period lasting roughly from 1300 to 1850 AD. It was not a true ice age like a Quaternary glacial period, but many regions had colder winters and shorter growing seasons.

Evidence includes:

• paintings showing larger Alpine glaciers
• records of harsh winters in Europe
• Thames Frost Fairs in London, when the River Thames froze during some severe winters
• tree-ring evidence showing slower growth in colder years

Modern warming

Modern warming refers to the strong rise in global average temperature since around 1850, especially since the mid-20th century. Global temperature data shows that Earth is now about 1.1–1.3°C warmer than the late 19th century, depending on the dataset used.

This period is different from earlier changes because it is:

• measured directly by instruments across the world
• rapid compared with many earlier natural changes
• global in pattern, not just regional

Evidence for climate change

Scientists use different evidence depending on the time period being studied. Some evidence is direct, meaning it measures climate itself. Other evidence is proxy evidence, meaning it gives an indirect clue.

Global temperature data

Global temperature data comes from thermometers at weather stations, ships, ocean buoys and satellites. It is the most direct evidence for recent climate change.

Reliable global records go back to around 1850. They show a clear warming trend, with the warmest years mostly occurring in the 21st century.

Scientists often use temperature anomalies rather than raw temperatures.

Using anomalies makes it easier to compare places with very different climates. For example, Antarctica and the Sahara have very different actual temperatures, but both can be compared by asking how much warmer or colder they are than normal for that place.

Ice cores

An ice core is a long cylinder of ice drilled from an ice sheet, such as those in Antarctica or Greenland. Snow falls, becomes compressed into ice, and traps tiny air bubbles.

Ice cores can show climate conditions hundreds of thousands of years into the past. Antarctic ice cores, such as the Vostok and EPICA cores, provide evidence for repeated glacial and interglacial cycles.

They are useful because they contain:

• trapped gases, such as carbon dioxide and methane
• oxygen isotopes, which help estimate past temperature
• dust and volcanic ash, which can show drier, windier or volcanic periods
• annual layers in some sections, rather like pages in a book

Tree rings

Tree-ring study is called dendrochronology. Many trees grow one ring each year. Wider rings often suggest better growing conditions, while narrower rings may suggest colder or drier conditions.

Tree rings are useful for reconstructing climate over hundreds or thousands of years. They are especially helpful in places where tree growth is strongly limited by temperature or rainfall.

However, tree rings need careful interpretation because growth can also be affected by disease, fire, soil conditions and the age of the tree.

Paintings and diaries

Paintings, diaries and written records are forms of historical evidence. They are useful for the last few centuries, especially before widespread thermometer records.

Examples include:

• paintings showing Alpine glaciers extending further down valleys during the Little Ice Age
• diaries describing severe winters, late harvests or frozen rivers
• records of harvest dates, which can suggest warmer or cooler growing seasons

This evidence is valuable because it gives human observations from the time. However, it is often local, incomplete and sometimes subjective.

Bringing it together

For this section, think in layers of time:

• Millions of years: the Quaternary period shows repeated glacial and interglacial cycles.
• Thousands of years: the Holocene is the current warm interglacial.
• Last 1,000 years: medieval warming, the Little Ice Age and modern warming show shorter-term changes.
• Last 150 years: direct global temperature data shows rapid modern warming.

The exam may ask you to describe climate change, compare periods, or explain how evidence shows climate has changed. Strong answers use dates, named evidence and careful wording.