WHITE MOUNTAINS INSURANCE GROUP LTD

ARK/WM OUTRIGGER

The Ark/WM Outrigger segment consists of Ark Insurance Holdings Limited and its subsidiaries (collectively, “Ark”) and Outrigger Re Ltd. Segregated Account 2023-1 (“WM Outrigger Re”) (collectively with Ark, “Ark/WM Outrigger”).

On January 1, 2021, White Mountains acquired a controlling ownership interest in Ark (the “Ark Transaction”). Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products, including property, specialty, marine & energy, casualty and accident & health.

During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd., a Bermuda company registered as a special purpose insurer and segregated accounts company, to provide collateralized reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2023 underwriting year. During the fourth quarter of 2023, Ark renewed the Outrigger Re Ltd. quota share agreement for the 2024 underwriting year.

Ark

Ark is a specialty property and casualty insurance and reinsurance company that offers a wide range of niche insurance and reinsurance products. Ark underwrites select coverages through its two major subsidiaries in the United Kingdom and Bermuda.

In the United Kingdom, Ark participates in the Lloyd’s of London (“Lloyd’s”) market through Ark Corporate Member Limited (“ACML”), Ark’s wholly-owned Lloyd’s corporate member, which in turn provides underwriting capacity to Lloyd’s Syndicates 4020 and 3902 (the “Syndicates”). Ark Syndicate Management Limited (“ASML”), Ark’s wholly-owned Lloyd’s managing agent, oversees the underwriting of the Syndicates. The Syndicates underwrite a diversified portfolio of insurance and reinsurance, including property, specialty, marine & energy, casualty and accident & health. Syndicate 4020 commenced underwriting on April 1, 2007 and Syndicate 3902 on January 1, 2017.

For the years of account prior to the Ark Transaction, a significant proportion of the Syndicates’ underwriting capital was provided by third-party insurance and reinsurance groups (“TPC Providers”) using whole account reinsurance contracts with Ark’s corporate member. For the years of account subsequent to the Ark Transaction, Ark is no longer using TPC Providers to provide underwriting capital for the Syndicates.

In January 2021, in response to an improved underwriting environment and with the capital provided from the Ark Transaction, Ark converted its wholly-owned subsidiary Group Ark Insurance Limited (“GAIL”) into a Class 4 Bermuda-domiciled insurance and reinsurance company and began to underwrite third-party business. Prior to this conversion, GAIL had been a Class 3 Bermuda-domiciled reinsurance company that only underwrote intercompany quota share reinsurance with ACML and provided additional capital to support ACML’s capital requirements at Lloyd’s (“Funds at Lloyd’s”). As a result of the Ark Transaction, GAIL underwent significant expansion of operations during 2021, with the recruitment of staff and enhancement of operations, to support this growth. GAIL underwrites a range of third-party business from Bermuda including property, specialty, marine & energy and casualty lines. In December 2023, AM Best affirmed Ark’s financial strength rating at “A/stable.”

In both jurisdictions, Ark underwrites business primarily through insurance and reinsurance brokers and wholesalers, both in the open market and through managing general agencies (“MGA”).

As of December 31, 2023 and 2022, White Mountains reported $4,133 million and $3,486 million of total assets and $1,230 million and $965 million of total equity related to Ark. As of December 31, 2023 and 2022, White Mountains owned 72.0% of Ark on a basic shares outstanding basis (61.9% and 63.0% after taking account of management’s equity incentives) and reported $337 million and $248 million of noncontrolling interests related to Ark. The remaining shares are owned by current and former employees. In the future, management rollover shareholders could earn additional shares in Ark if and to the extent that White Mountains achieves certain thresholds for its multiple of invested capital return. If fully earned, these additional shares would represent 12.5% of the shares outstanding at closing.

During the fourth quarter of 2022, Ark sponsored the formation of Outrigger Re Ltd., a Bermuda company registered as a special purpose insurer and segregated accounts company, to provide reinsurance capacity to Ark. On December 20, 2022, Outrigger Re Ltd. issued $250 million of non-voting redeemable preference shares on behalf of four segregated accounts to White Mountains and unrelated third-party investors, of which $205 million was provided by White Mountains. Upon issuance of the preference shares, Outrigger Re Ltd. entered into collateralized quota share agreements with GAIL to provide reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2023 underwriting year. The proceeds from the issuance of the preference shares were deposited into collateral trust accounts to fund any potential obligations under the reinsurance agreements with GAIL. Outrigger Re Ltd.’s obligations under the reinsurance agreements with GAIL are subject to an aggregate limit equal to the assets in the collateral trusts. The terms of the reinsurance agreements are renewable upon the mutual agreement of Ark and the applicable preference shareholder of Outrigger Re Ltd.

During the fourth quarter of 2023, Ark renewed Outrigger Re Ltd. to provide reinsurance protection on Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2024 underwriting year. Outrigger Re Ltd. was capitalized with $250 million for business written in the 2024 underwriting year, of which White Mountains rolled over $130 million from its commitment to the 2023 underwriting year. The remaining capital was provided by new and continuing unrelated third-party investors.

During January 2024, White Mountains received an initial return of capital of $68 million from WM Outrigger Re for business written in the 2023 underwriting year. White Mountains expects to receive any additional return of capital and associated profits from business written in the 2023 underwriting year beginning in the second quarter of 2024.

As of December 31, 2023 and 2022, White Mountains reported $294 million and $205 million of total assets and $273 million and $204 million of total equity related to WM Outrigger Re. As of December 31, 2023 and 2022, White Mountains owned 100% of WM Outrigger Re’s preferred equity.

Insurance and Reinsurance Overview

Generally, insurance companies underwrite insurance policies in exchange for premiums paid by their customers (the insureds). An insurance policy is a contract between the insurance company and the insured where the insurance company agrees to pay for losses suffered by the insured or a third-party claimant that are covered under the contract. Such contracts are often subject to subsequent legal interpretation by courts, legislative action, and arbitration.

Reinsurance is an arrangement in which a reinsurance company (the reinsurer) agrees to indemnify an insurance company (the ceding company) for insurance risks underwritten by the ceding company. Reinsurance can benefit a ceding company in several ways, including reducing net exposure to individual risks, providing protection from large or catastrophic losses and assisting in maintaining required capital levels and financial or operating leverage ratios. Reinsurance can provide a ceding company with additional underwriting capacity by permitting it to accept larger risks and underwrite a greater number of risks without increasing its capital as much as would be the case without reinsurance. Reinsurers themselves, may also purchase reinsurance, which is known as retrocessional reinsurance to cover risks assumed from ceding companies. Reinsurance companies often enter into retrocessional reinsurance agreements for many of the reasons that ceding companies enter into reinsurance agreements.

Reinsurance is generally written on a treaty or facultative basis. Treaty reinsurance is an agreement whereby the reinsurer assumes a specified portion or category of risk under all qualifying policies issued by the ceding company during the term of the agreement, usually one year. When underwriting treaty reinsurance business, the reinsurer does not evaluate each individual risk and generally accepts the original underwriting decisions made by the ceding company. Treaty reinsurance is typically written on either a proportional or excess of loss basis. A proportional reinsurance treaty is an arrangement whereby a reinsurer assumes a predetermined proportional share of the premiums and losses generated on specified business. An excess of loss treaty is an arrangement whereby a reinsurer assumes losses that exceed a specific retention of loss by the ceding company. Facultative reinsurance, on the other hand, is underwritten on a risk-by-risk basis, which allows the reinsurer to determine individual pricing for each exposure.

Insurance and reinsurance companies incur a significant amount of their total expenses from policy obligations, which are commonly referred to as claims or losses. In settling claims, various LAE are incurred such as insurance adjusters’ fees and litigation expenses. Losses and LAE are categorized by the year in which the policy is underwritten (the year of account or underwriting year) for purposes of Ark’s claims management and estimation of the ultimate loss and LAE reserves. For purposes of Ark’s reporting under GAAP, losses and LAE are categorized by the year in which the claim is incurred (the accident year). In the following calendar years, as Ark increases or decreases its estimate for the ultimate loss and LAE for claims in prior underwriting years, or prior accident years for reporting under GAAP, it will record favorable or unfavorable loss reserve development, which is recorded in the calendar year when such loss reserve development is determined. In addition, insurance companies incur policy acquisition expenses, such as commissions paid to agents and premium taxes, and other expenses related to the underwriting process, including employee compensation and benefits. A key measure of absolute and relative underwriting performance for an insurance company is the combined ratio. An insurance company’s combined ratio is calculated by adding the ratio of incurred loss and LAE to earned premiums (the loss ratio) and the ratio of policy acquisition and other underwriting expenses to earned premiums (the expense ratio). A combined ratio under 100% indicates that an insurance company is generating an underwriting profit, while a combined ratio over 100% indicates that an insurance company is generating an underwriting loss.

Ark derives substantially all of its revenues from earned premiums, investment income and net realized and unrealized investment gains (losses). Written premiums represent the amount charged to an insured or reinsured party to provide coverage under an insurance or reinsurance contract, which are recognized as earned premiums within revenue over the period that insurance coverage period is provided (i.e., ratably over the life of the policy or, in the case of catastrophe premiums, in proportion to the level of insurance protection provided.) Unearned premiums represent the portion of premiums written that are applicable to future insurance coverage provided by policies. A significant period often elapses between receipt of insurance premiums and payment of insurance claims. During this time, Ark invests the premiums, earns investment income and generates net realized and unrealized investment gains (losses).

Lines of Business

Ark writes specialized lines of insurance and reinsurance across its United Kingdom and Bermuda platforms within five major lines of business: property, specialty, marine & energy, casualty and accident & health. Claims for property, specialty, marine & energy and accident & health coverages are typically reported and settled in a relatively short period of time. Casualty insurance (often referred to as liability insurance) generally covers the financial consequences of a legal liability of an individual or an organization resulting from negligent acts or omissions causing bodily injury, property damages and/or economic damages to a third-party. Settlements for casualty/liability coverages can extend for long periods of time as claims are often reported and ultimately paid or settled years after the related loss events occur.

Ark has recently added, and expects to continue to add, new business to its portfolio, as it focuses on profitable business opportunities while carefully managing underwriting risk. Ark also leads two Lloyd’s market consortia that target renewable energy clients including wind farms, solar plants, hydroelectric plants, geothermal plants and wave and tidal projects.

The following table presents Ark’s gross written premiums by line of business for the years ended December 31, 2023, 2022 and 2021:

A description of Ark’s business written within each line of business follows:

Property

Ark’s property business is underwritten on both an insurance and reinsurance basis covering the financial consequences of accidental losses to an insured’s property, such as a business’s building, inventory and equipment, or personal property. Coverages provided include all risks of direct physical loss or damage, business interruption and natural and non-natural catastrophe perils. Ark’s property insurance business consists primarily of direct and facultative contracts, line slips and MGA binding authorities. Ark’s property insurance business is underwritten on a worldwide basis with a focus on excess & surplus lines in the United States and on large international accounts. Ark’s property reinsurance business consists primarily of treaty reinsurance underwritten on a catastrophe excess of loss, per risk excess and proportional basis. Ark’s property reinsurance business is underwritten on a worldwide basis with particular focus on risks in the United States, Europe and Asia.

Specialty

Ark’s specialty business is underwritten on both an insurance and reinsurance basis covering a range of individual risks and treaties primarily including aviation, space, political and credit, cyber, terrorism and political violence, product defect and contamination, nuclear, fine art & specie, surety and mortgage. Ark’s specialty insurance and reinsurance business is underwritten on a worldwide basis.

Aviation

Aviation insurance primarily covers airlines and general aviation for loss of, or damage to, aircraft hull and ensuing passenger and third-party liability. Perils include war and war-like actions such as terrorism. Additionally, liability arising out of non-aircraft operations such as hangars and airports may be covered.

Space

Space insurance primarily covers loss of, or damage to, satellites during launch and in orbit, including faulty design that leads to early loss of operating life. Ark’s space insurance is primarily written through binders supporting specialized, technical MGAs.

Political and Credit

Political and credit insurance primarily covers risks relating to the confiscation, expropriation, nationalization and deprivation of insured assets due to war, political, or government action as well as contract frustration and non-payment by obligors.

Cyber

Cyber insurance primarily covers the physical damage and liabilities arising from cyber attacks, including coverage for ransomware, loss of data and third-party liabilities.

Terrorism and Political Violence

Terrorism and political violence insurance primarily covers physical loss or damage and threat thereof, including ensuing loss through business interruption, caused by declared terror events, political violence, and war and war-like actions in developed and developing countries around the world.

Product Defect and Contamination

Product defect and contamination insurance primarily covers first and third-party costs associated with product recall or contamination including malicious product tampering, product safety, or government mandated recall. Ark’s product defect and contamination insurance covers a wide range of industries including food & beverage, manufacturing, and consumer products.

Nuclear

Nuclear insurance covers country specific nuclear pools and companies and institutions with nuclear exposure excluded from standard property and casualty policies for coverage of physical damage and third-party liability.

Fine Art & Specie

Fine art & specie insurance primarily covers loss to fine art, specie, cash in transit and vault, and jewelers’ block risks as a result of theft or damage in transit or at exhibition.

Surety

Surety insurance covers financial guarantee risks between a bond issuer, principal and obligee designed to address responsibility for debt payments, default or other financial obligations. Ark underwrites this portfolio on a reinsurance basis, primarily excess of loss, for U.S. domiciled clients. The underlying assureds cover a variety of industries including construction, oil & gas, hotel & leisure, and transportation projects.

Mortgage

Mortgage insurance covers financial guarantee risks between a lending institution and a borrower designed to address responsibility for debt payments and default. Ark underwrites a small reinsurance book on behalf of one client for government-sponsored enterprises that offer insurers excess of loss credit insurance coverage on mortgage loans via Fannie Mae’s Credit Insurance Risk Transfer and Freddie Mac’s Agency Credit Insurance Structure programs.

Marine & Energy

Ark’s marine & energy business is underwritten on both an insurance and reinsurance basis primarily covering marine hull, cargo, specie, marine & energy liabilities and upstream energy platform physical damage and liability. Marine hull consists primarily of coastal and ocean-going vessels and covers worldwide risks on an all perils or total loss only basis together with lighter craft, including yachts. Cargo consists of worldwide transits and moveable goods with a particular emphasis on bulk cargo, project cargo and pre-launch satellite risks. Specie is the transit and storage of high value goods including semi-precious and precious metals. Marine & energy liabilities consists of liability risks arising from doing business in their respective industries including liabilities arising from pollution and damage covered by protection and indemnity clubs, including for example the International Group of Protection & Indemnity Clubs. Upstream energy platform physical damage and liability covers a variety of oil and gas industry construction, exploration and production risks.

Ark’s marine & energy insurance business consists of direct and facultative risks written primarily in the open market, as well as through line slips and MGA binding authorities. Ark’s marine & energy reinsurance business consists of treaty reinsurance underwritten on both a proportional and excess of loss basis. Ark’s marine & energy insurance and reinsurance business is underwritten on a worldwide basis.

Casualty

Ark’s casualty business is underwritten on an insurance and reinsurance basis primarily covering medical malpractice, professional liability and general liability. Ark’s casualty insurance business is generally written on an excess of loss basis arising from operations of a wide range of predominantly large U.S. companies, including energy companies, with global operations. Ark’s casualty reinsurance business is underwritten on an excess of loss and proportional treaty basis.

Accident & Health

Ark’s accident & health business is underwritten on both an insurance and reinsurance basis covering a wide range of personal accident, sickness, disability, travel and medical insurance risks. Ark’s accident & health insurance business consists of direct and facultative contracts written in the open market and through Accident & Health Underwriting Limited (“AHU”), Ark’s wholly-owned MGA domiciled in the United Kingdom. Ark’s accident & health insurance and reinsurance business is underwritten on a worldwide basis.

Geographic Concentration

The following table shows Ark’s gross written premiums by geographic region based on the location of Ark’s underwriting offices for the years ended December 31, 2023, 2022 and 2021:

Marketing and Distribution

Ark offers its products and services through a network of brokers, MGAs and reinsurance intermediaries (collectively, “insurance and reinsurance intermediaries”). In the United Kingdom, Ark operates through the Syndicates with Lloyd’s approved brokers and MGAs. In Bermuda, Ark primarily derives its reinsurance business through reinsurance intermediaries that represent the ceding company and its insurance business through brokers based in Bermuda and London. Ark pays acquisition costs to brokers, MGAs and reinsurance intermediaries as compensation for facilitating the flow and processing of business, typically on industry standard percentages of premium underwritten. In addition, Ark pays certain MGAs profit commissions based on the underwriting profit of the business they produce.

During the years ended December 31, 2023, 2022 and 2021, Ark received a significant portion of its gross written premiums from four insurance and reinsurance intermediaries. The following table shows the proportion of business produced by the top four insurance and reinsurance intermediaries for the years ended December 31, 2023, 2022 and 2021:

Underwriting and Pricing

Ark aims to build a diversified and balanced portfolio of risks that generates an underwriting profit each year. Ark believes in a disciplined underwriting strategy that aims to consistently outperform the market. In hard market conditions, Ark aims to grow premiums rapidly, as pricing, terms and conditions and limit deployment are more favorable and can lead to enhanced returns on capital. In soft markets, Ark is willing to reduce its business volume when pricing, terms and conditions and limit deployment can make it more difficult to achieve an adequate return on capital. Ark is willing to forgo business if it believes it is not priced appropriately for the exposure or risk assumed.

Ark operates an underwriting controls framework which includes individual underwriting authorities, continual quality monitoring and peer review of risks. The framework aims to ensure a high quality of underwriting through monitoring of pricing and rate change, contract certainty and appropriate terms and conditions. The nature of delegated underwriting naturally increases the risk of underwriting, through the ability of third parties being able to bind Ark to risks without detailed review of the risk involved. This risk is mitigated through the application of strict guidelines, managed by a dedicated team within the Ark compliance department. This team reviews MGA and third-party binding authority approvals pre-bind and monitors a program of audits to ensure compliance with regulations and guidelines.

Ark uses bespoke pricing models for each of the products that it underwrites. These pricing models seek to generate a pricing metric required to achieve an acceptable return on capital for each class of business, and each of the risks priced therein. These models rely on several factors depending on the class of business, including exposure analysis, historical experience, estimates of future loss costs, claims experience and natural catastrophe outlook, including the physical risk of climate change and inflation. See“Ark — Catastrophe Risk Management and Reinsurance Protection” on page 13.

Ark actively monitors price adequacy at various points between individual risks and the portfolio level to measure and evaluate overall performance. In addition, Ark updates rates to achieve targeted returns on capital at an individual risk as well as portfolio level to enhance return on capital.

Competition

Specialized lines of insurance and reinsurance are highly competitive. Ark competes with other Lloyd’s syndicates, London market participants and major U.S., Bermuda, European and other international insurance and reinsurance companies. The significant competitive factors for most products are price, terms and conditions, broker relationships, underwriting service, rating agency financial strength rating, and claims service. Ark competes with insurance and reinsurance companies who operate in the Bermuda and Lloyd’s markets such as:

•Bermuda insurance and reinsurance market: American International Group, Inc., Arch Capital Group Ltd., Aspen Insurance Holdings Ltd., Everest Re Group, RenaissanceRe Holdings Ltd. and others;

•Lloyd’s market: MS Amlin Ltd, Lancashire Holdings Ltd, Beazley plc, Hiscox plc, and other syndicates.

Claims Management

Effective claims management is a critical factor in achieving satisfactory underwriting results. Ark maintains an experienced staff of dedicated claims handlers and loss adjusters. These individuals seek to ensure that Ark has the appropriate level of expertise to handle complex claims. Within the claims departments, Ark also uses various shared services. These include third-party claims administrators, particularly for lower value, less specialized claims (for example in Ark’s MGA produced business), subrogation and recovery support, and legal representation.

For business written in the Lloyd’s market, claims handling and case reserves are established in accordance with the applicable Lloyd’s Claim Scheme and Lloyd’s Claims Management Principles and Oversight Framework.

Catastrophe Risk Management and Reinsurance Protection

Catastrophe Risk Management

Ark

Ark has exposure to losses caused by unpredictable catastrophic events all over the world including natural and other disasters such as hurricanes, windstorms, earthquakes, floods, wildfires, tornadoes, tsunamis, and severe weather. Catastrophes can also include large losses driven by public health crises, terrorist attacks, war and war-like actions, explosions, infrastructure failures, and cyber attacks. The extent of a catastrophe loss is a function of both the severity of the event and total amount of insured exposure to the event, as well as the coverage provided to customers. Increases in the value and concentration of insured property or insured employees, the effects of inflation, changes in weather patterns and increased terrorism and war and war-like actions could increase the future frequency and/or severity of claims from catastrophic events. Climate change, which is characterized by higher temperatures, sea level rise and more extreme weather events including droughts, heavy storms, wildfires and stronger hurricanes, increases the frequency and severity of certain major natural catastrophes. There is also a growing threat of cyber catastrophes due to the increasing interconnectivity of global systems.

Ark seeks to manage its exposure to catastrophic losses by limiting and monitoring the aggregate insured value of policies in geographic areas with exposure to catastrophic events and by buying reinsurance. To manage, monitor and analyze insured values and potential losses, Ark utilizes proprietary and third-party catastrophe management software to estimate potential losses for many different catastrophe scenarios. Ark incorporates the physical risk of climate change in its underwriting process through sensitivity and stress testing of its catastrophe models, including increased frequency of U.S. windstorms and the implications of storm surge.

Ark licenses third-party global property catastrophe models from Risk Management Solutions Inc. (“RMS”), as well as utilizing its own proprietary models to calculate expected probable maximum loss estimates (“PML”) from various property and non-property catastrophe scenarios. Ark prices property catastrophe contracts using its own proprietary models that can take inputs from third-party software and other data as appropriate. For business that Ark determines to have exposure to catastrophic perils, as part of its underwriting process, it models and evaluates the exposure to assess whether there is an appropriate premium charged for the exposure assumed.

Ark’s two largest natural catastrophe PML zones on a per occurrence basis for a 1-in-250 year event as of January 2024, as measured on a net after-tax exposure basis, are U.S. windstorm and U.S. earthquake. The net after-tax exposure is net of amounts ceded to reinsurers and reinstatement premiums. Different perils are more prevalent at different times of the year, and Ark tailors its outwards reinsurance program to incept accordingly throughout the year. Once the placement of Ark’s 2024 outwards reinsurance program is completed, Ark expects its net after-tax exposure for a 1-in-250 year event to each of these PML zones to approximate 25-35% of total tangible capital (tangible shareholders equity and subordinated debt). Total tangible capital was $1,261 million as of December 31, 2023.

In addition, Ark also has loss exposures to other global natural catastrophe events including, but not limited to, Japanese earthquakes, Japanese windstorms, European windstorms, and U.S. wildfires.

Ark’s estimates of potential losses are dependent on many variables, including assumptions about storm intensity, storm surge, and loss amplification, loss adjustment expenses and insurance-to-value in the aftermath of weather-related catastrophes. In addition, Ark has to account for quality of data provided by insureds. Accordingly, if the assumptions are incorrect, the losses Ark might incur from an actual catastrophe could be materially different than the expectation of losses generated from modeled catastrophe scenarios. There could also be unmodelled losses which exceed the amounts estimated for U.S. windstorm and U.S. earthquake catastrophes.

Outside of natural catastrophe losses, Ark has exposure to non-natural or man-made large losses. Ark uses data from clients and combines this with accumulation tools and PML assessments to obtain potential loss scenarios. The current largest exposures are cyber, offshore energy production platforms, terrorism events, war and war-like actions and political risk.

Cyber losses can be derived from a number of scenarios that include major data security breach on large multinational organizations, business blackout from cyber attack on power generation and distribution facilities, malicious attack on cloud service provider data center and ransomware contagion across both individual and multiple corporations. Catastrophic losses in respect of offshore energy production facilities can include physical damage, business interruption, pollution liability, extra expenses and control of oil or gas flow therefrom. Terrorism and war and war-like actions can include physical damage, business interruption, liability, loss of life and fire following at locations around the world either in a single city or in coordinated attacks across multiple cities, countries or regions. Political risk scenarios can include confiscation, expropriation, nationalization and deprivation of assets, non-payment of obligations, political violence and war derived from geo-political instability, country overthrow and commodity price movement. Ark estimates its largest net after-tax loss from non-natural/man-made loss scenarios to be approximately 12% of total tangible capital.

Effective January, 1, 2023, through its quota share reinsurance agreement with GAIL, WM Outrigger Re has exposure to losses caused by unpredictable catastrophic events including natural and other disasters all over the world such as hurricanes, windstorms, earthquakes, floods, wildfires, tornadoes, tsunamis, severe weather, and infrastructure failures. The extent of a catastrophe loss is a function of both the severity of the event and total amount of insured exposure to the event, as well as the coverage provided to customers. Increases in the value and concentration of insured property, the effects of inflation and changes in weather patterns could increase the future frequency and/or severity of claims from catastrophic events. Climate change, which is characterized by higher temperatures, sea level rise and more extreme weather events including droughts, heavy storms, wildfires and stronger hurricanes, increases the frequency and severity of certain major natural catastrophes.

WM Outrigger Re’s two largest natural catastrophe PML zones on a per occurrence basis for a 1-in-250 year event as of January 2024, as measured on a net after-tax exposure basis, are U.S. windstorm and U.S. earthquake. WM Outrigger Re’s obligations under the reinsurance agreement with GAIL are subject to an aggregate limit equal to the assets in the collateral trust at any point in time.

When considering both Ark and WM Outrigger Re, White Mountains’s two largest natural catastrophe PML zones on a per occurrence basis for a 1-in-250 year event as of January 2024, as measured on a net after-tax exposure basis, are U.S. windstorm and U.S. earthquake. The net after-tax exposure is net of amounts ceded to reinsurers and reinstatement premiums. Different perils are more prevalent at different times of the year, and Ark tailors its outwards reinsurance program to incept accordingly. Once the placement of Ark’s 2024 outwards reinsurance program is completed, White Mountains expects its consolidated net after-tax exposure for a 1-in-250 year event to each of these PML zones will be roughly 10% of White Mountains’s common shareholders’ equity as of December 31, 2023.

Reinsurance Protection

As part of its enterprise risk management function, Ark purchases reinsurance for risk mitigation purposes. Ark utilizes reinsurance and retrocession agreements to reduce earnings volatility, protect capital, limit its exposure to risk concentration and accumulation of loss and manage within its overall internal risk tolerances or those set and agreed by regulators, ratings agencies and Lloyd’s. Ark also enters into reinsurance and retrocession agreements to reduce its liability on individual risks and enable it to underwrite policies with higher limits where Ark believes this has a broader business benefit.

Ark seeks to protect its downside risk from catastrophes and large loss events by purchasing reinsurance, including quota share and excess of loss protections, aggregate covers, and industry loss warranties. Ark also considers alternative structures such as collateralized reinsurance, retrocessional reinsurance and catastrophe bonds.

During the fourth quarter of 2022, Ark entered into a 40% collateralized quota share agreement with Outrigger Re Ltd., a Bermuda special purpose insurer, covering Ark’s Bermuda global property catastrophe excess of loss portfolio written in the 2023 underwriting year. During the fourth quarter of 2023, Ark renewed the Outrigger Re Ltd. quota share agreement for the 2024 underwriting year.

The purchase of reinsurance does not discharge Ark from its primary liability for the full value of its policies, and thus the collectability of balances due from Ark’s reinsurers is critical to its financial strength. Ark monitors the financial strength and ratings of its reinsurers on an ongoing basis. See Note 6 — “Third-party Reinsurance” on page F-45 for a discussion of Ark’s top reinsurers.

Ark’s Loss and LAE Reserves

Ark establishes loss and LAE reserves that are estimates of amounts needed to pay claims and related expenses in the future for insured events that have already occurred, including both reported and unreported claims. Loss reserves are established due to the significant periods of time that may occur between the occurrence, reporting and payment of a loss. The process of estimating reserves involves a considerable degree of judgment by management and is inherently uncertain. See “CRITICAL ACCOUNTING ESTIMATES — Loss and LAE Reserves” on page 79 and Note 5 — “Loss and Loss Adjustment Expense Reserves” on page F-33 for a full discussion regarding Ark’s loss reserving process.